dol.trans

Tools to wrap stores with key/value transforms, filters, caches and other layers.

A wrap leaves the backend untouched and builds a new class (or instance) around it. The decorators built with store_decorator (wrap_kvs, filt_iter, cached_keys, add_path_access, …) can be applied to a class, to an instance, or used as a factory (deco(**params)(store)).

Main entry points:

• wrap_kvs: key/value transforms (key_of_id, obj_of_data, codecs, …)

• filt_iter: restrict a store to a subset of its keys

• cached_keys: cache the key listing of a slow store

• add_path_access: read/write nested stores through key paths

• kv_wrap: wrap using an object that holds _id_of_key/_obj_of_data-style methods

  >>> from dol.trans import wrap_kvs
  >>> s = wrap_kvs({}, key_of_id=str.upper, id_of_key=str.lower, obj_of_data=int, data_of_obj=str)
  >>> s['a'] = 1
  >>> s.store  # the backend holds the transformed key and value
  {'a': '1'}
  >>> list(s), s['A']
  (['A'], 1)
  

Module Attributes

confirm_overwrite(self, k, v)

A ready-to-use wrap_kvs preset that asks (via the builtin input) to confirm before overwriting an existing key with a different value (Issue #13).

Functions

add_aliases(obj, **aliases)	A function that wraps the object instance and adds aliases.
add_decoder([store_cls, decoder, name, ...])	Add a decoder layer to a store.
add_ipython_key_completions(store)	Add tab completion that shows you the keys of the store.
add_missing_key_handling([store, ...])	Overrides the __missing__ method of a store with a custom callback.
add_path_access([store, name, path_type, ...])	Make nested stores (read/write) accessible through key paths (iterable of keys).
add_path_get([store, name, path_type, ...])	Make nested stores accessible through key paths.
add_store_method(store, *, method_func[, ...])	Add methods to store classes or instances
add_wrapper_method([wrap_cls, method_name])	Decorator that adds a wrapper method (itself a decorator) to a wrapping class Clear? See mk_wrapper function and doctest example if not.
affix_key_codec([prefix, suffix])	A factory that creates a key codec that affixes a prefix and suffix to the key
assert_min_num_of_args(func, num_of_args)	Assert that a function can be a store method.
autoviv([store])	Opt-in write-through autovivification for key-paths.
cache_iter([store, keys_cache, ...])	Make a class that wraps input class's __iter__ becomes cached.
cached_keys([store, keys_cache, ...])	Make a class that wraps input class's __iter__ becomes cached.
catch_and_cache_error_keys([store, ...])	Store that will cache keys as they're accessed, separating those that raised errors and those that didn't.
condition_function_call([func, condition, ...])	Decorator: call func only when condition(*args, **kwargs) holds, else callback_if_condition_not_met.
conditional_data_trans([store, __module__, ...])	Wrap store so that data_trans is applied to the read values satisfying condition (others pass through).
confirm_overwrite(self, k, v)	A ready-to-use wrap_kvs preset that asks (via the builtin input) to confirm before overwriting an existing key with a different value (Issue #13).
constant_output([return_val])	Function that returns a constant value no matter what the inputs are.
disable_delitem(o)	Replace o.__delitem__ (if any) with a function raising ValueError.
disable_setitem(o)	Replace o.__setitem__ (if any) with a function raising ValueError.
disallow_overwrites(store, *[, error_msg, ...])	Return a subclass of store whose __setitem__ raises OverWritesNotAllowedError on existing keys (store itself is left untouched).
double_up_as_factory(decorator_func)	Repurpose a decorator both as it's original form, and as a decorator factory.
ensure_clear_method([store, clear_method])	If obj doesn't have an enabled clear method, will add one (a slow one that runs through keys and deletes them
ensure_set(x)	A set from x, treating a string as a single element.
filt_iter([store, filt, name, __module__, ...])	Make a wrapper that will transform a store (class or instance thereof) into a sub-store (i.e. subset of keys).
filter_prefixes(prefixes)	Make a filter that returns True if a string starts with one of the given prefixes
filter_regex(regex, *[, return_search_func])	Make a filter that returns True if a string matches the given regex
filter_suffixes(suffixes)	Make a filter that returns True if a string ends with one of the given suffixes
flatten([store, levels, cache_keys, ...])	Give a nested store a flat view whose keys are the (a, b, c) key paths.
get_class_name(cls[, dflt_name])	The __qualname__ of cls (or of its class), else dflt_name; raises ValueError if there is neither.
ignore_if_error([store, errors])	Wrap store so that __getitem__ errors in errors return None instead of raising.
insert_aliases([store, write, read, delete, ...])	Insert method aliases of CRUD operations of a store (class or instance).
insert_hash_method([store, hash_method, ...])	Make a store hashable using the specified hash_method.
insert_load_dump_aliases([store, delete, ...])	Insert load and dump methods, with familiar dump(obj, location) signature.
is_iterable(x)	Whether x is an Iterable.
iterate_values_and_accumulate_non_error_keys(...)	Yield the values of store, appending to cache_keys_here the keys whose value was fetched without error.
kv_wrap(trans_obj)	A function that makes a wrapper (a decorator) that will get the wrappers from methods of the input object.
kv_wrap_persister_cls(persister_cls[, name])	Make a class that wraps a persister into a dol.base.Store,
leveled_paths_walk(m, levels)	Yield the key paths of m, down to levels levels.
mk_confirm_overwrite_preset(*[, get_input, ...])	Make a wrap_kvs preset that asks for confirmation before overwriting an existing key that holds a different value.
mk_kv_reader_from_kv_collection(kv_collection)	Make a KvReader class from a Collection class.
mk_level_walk_filt(levels)	Makes a walk_filt function for kv_walk based on some level logic.
mk_read_only(o)	Disable __setitem__ and __delitem__ on o (a store class, typically).
mk_trans_obj(**kwargs)	Convenience method to quickly make a trans_obj (just an object holding some trans functions
mk_wrapper(wrap_cls)	You have a wrapper class and you want to make a wrapper out of it, that is, a decorator factory with which you can make wrappers, like this:
raise_disabled_error(functionality)	Make a function that raises ValueError('<functionality> is disabled') whenever called.
redirect_getattr_to_getitem([cls, ...])	A mapping decorator that redirects attribute access to __getitem__.
return_default_if_error([store, default, errors])	Wrap store so that __getitem__ errors in errors return default instead of raising.
store_decorator(func)	Helper to make store decorators.
store_wrap(obj)	Wrap a class or an instance in a Store (a class gets a Store subclass whose __init__ builds the wrapped instance).
take_everything(key)	Key filter that accepts every key.
transparent_key_method(self, k)	Return the key as is (the default getitem of mk_kv_reader_from_kv_collection).
warn_and_ignore_if_error([store, errors, ...])	Like ignore_if_error, but also emit a warning (warn_msg) for each ignored error.
wrap_kvs([store, wrapper, name, key_of_id, ...])	Make a Store that is wrapped with the given key/val transformers.

Classes

CachedInvertibleTrans(trans_func)
Codec(encoder, decoder)	An encoder/decoder pair; iterates as (encoder, decoder) and composes with compose_with.
FiltIter(*args, **kwargs)	Namespace of filt_iter factories (regex, suffixes, ...); not meant to be instantiated.
FirstArgIsMapping(val)	Mark a transform so its first argument is the store (mapping), not the data.
KeyCodec(encoder, decoder)	A Codec that, called on a store, wraps its keys (id_of_key/key_of_id).
KeyValueCodec(encoder, decoder)	A Codec that, called on a store, wraps values with key context (preset/postget).
OverWritesNotAllowedMixin()	Mixin for only allowing a write to a key if they key doesn't already exist.
SimpleDelegator(obj)	Forward attribute access (and calls) to the wrapped obj.
ValueCodec(encoder, decoder)	A Codec that, called on a store, wraps its values (data_of_obj/obj_of_data).

Exceptions

MapInvertabilityError

To be used to indicate that a mapping isn't, or wouldn't be, invertible

class dol.trans.CachedInvertibleTrans(trans_func)

Bases: object

>>> t = CachedInvertibleTrans(lambda x: x[1])
>>> t.ingress('ab')
'b'
>>> t.ingress((1, 2))
2
>>> t.egress('b')
'ab'
>>> t.egress(2)
(1, 2)

class dol.trans.Codec(encoder, decoder)

Bases: Generic[DecodedType, EncodedType]

An encoder/decoder pair; iterates as (encoder, decoder) and composes with compose_with.

invert()

Return a codec that is the inverse of this one. That is, encoder and decoder will be swapped.

class dol.trans.FiltIter(*args, **kwargs)

Bases: object

Namespace of filt_iter factories (regex, suffixes, …); not meant to be instantiated.

prefixes()

Make a mapping-filtering decorator that filters keys with a prefixes.

Parameters:

prefixes – A string or iterable of strings that are the prefixes to filter

>>> is_test = filt_iter.prefixes('test')
>>> d = {'test.txt': 1, 'report.doc': 2, 'test_image.jpg': 3}
>>> dd = is_test(d)
>>> dict(dd)
{'test.txt': 1, 'test_image.jpg': 3}

regex()

Make a mapping-filtering decorator that filters keys with a regex.

Parameters:

regex – A regex string or compiled regex

>>> contains_a = filt_iter.regex(r'a')
>>> d = {'apple': 1, 'banana': 2, 'cherry': 3}
>>> dd = contains_a(d)
>>> dict(dd)
{'apple': 1, 'banana': 2}

suffixes()

Make a mapping-filtering decorator that filters keys with a suffixes.

Parameters:

suffixes – A string or iterable of strings that are the suffixes to filter

>>> is_text = filt_iter.suffixes(['.txt', '.doc', '.pdf'])
>>> d = {'test.txt': 1, 'report.doc': 2, 'image.jpg': 3}
>>> dd = is_text(d)
>>> dict(dd)
{'test.txt': 1, 'report.doc': 2}

class dol.trans.FirstArgIsMapping(val)

Bases: LiteralVal

Mark a transform so its first argument is the store (mapping), not the data.

Use this to explicitly opt a transform function into the f(self, data) calling convention in wrappers such as wrap_kvs – instead of relying on the name/arity heuristic (_has_unbound_self()). This is the escape hatch for functions the heuristic can’t (or shouldn’t) infer, and the recommended, explicit alternative to naming a transform’s first parameter self/store/mapping.

>>> from dol import wrap_kvs, FirstArgIsMapping
>>> def prefix_with_name(self, data):
...     return f"{getattr(self, 'name', '?')}:{data}"
>>> S = wrap_kvs(dict, obj_of_data=FirstArgIsMapping(prefix_with_name))
>>> s = S({'a': 'x'}); s.name = 'ns'
>>> s['a']
'ns:x'

class dol.trans.KeyCodec(encoder, decoder)

Bases: Generic[DecodedType, EncodedType], Codec[DecodedType, EncodedType]

A Codec that, called on a store, wraps its keys (id_of_key/key_of_id).

class dol.trans.KeyValueCodec(encoder, decoder)

Bases: Generic[DecodedType, EncodedType], Codec[DecodedType, EncodedType]

A Codec that, called on a store, wraps values with key context (preset/postget).

exception dol.trans.MapInvertabilityError

Bases: ValueError

To be used to indicate that a mapping isn’t, or wouldn’t be, invertible

class dol.trans.OverWritesNotAllowedMixin

Bases: object

Mixin for only allowing a write to a key if they key doesn’t already exist.

Note

Should be before the persister in the MRO.

>>> class TestPersister(OverWritesNotAllowedMixin, dict):
...     pass
>>> p = TestPersister()
>>> p['foo'] = 'bar'
>>> #p['foo'] = 'bar2'  # will raise error
>>> p['foo'] = 'this value should not be stored'
Traceback (most recent call last):
  ...
dol.errors.OverWritesNotAllowedError: key foo already exists and cannot be overwritten.
    If you really want to write to that key, delete it before writing
>>> p['foo']  # foo is still bar
'bar'
>>> del p['foo']
>>> p['foo'] = 'this value WILL be stored'
>>> p['foo']
'this value WILL be stored'

class dol.trans.SimpleDelegator(obj)

Bases: object

Forward attribute access (and calls) to the wrapped obj.

class dol.trans.ValueCodec(encoder, decoder)

Bases: Generic[DecodedType, EncodedType], Codec[DecodedType, EncodedType]

A Codec that, called on a store, wraps its values (data_of_obj/obj_of_data).

dol.trans.add_aliases(obj, **aliases)

A function that wraps the object instance and adds aliases.

See also, and not to be confused with insert_aliases, which adds aliases to dunder mapping methods (like __iter__, __getitem__) etc.

dol.trans.add_decoder(store_cls=None, *, decoder=None, name=None, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Add a decoder layer to a store.

Note

This is a convenience function for wrap_kvs(..., obj_of_data=decoder).

>>> s = {'a': "42"}
>>> ss = add_decoder(s, decoder=int)
>>> ss['a']
42

If there’s only one callable argument, it is assumed to be the decoder:

>>> wrapper = add_decoder(int)
>>> S = wrapper(dict)
>>> sss = S({'a': "42"})
>>> dict(sss) == {'a': 42}
True

dol.trans.add_ipython_key_completions(store)

Add tab completion that shows you the keys of the store.

Note

ipython already adds local path listing automatically, so you’ll still get those along with your valid store keys.

dol.trans.add_missing_key_handling(store=None, *, missing_key_callback, errors_that_trigger_missing=(<class 'KeyError'>, ), __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Overrides the __missing__ method of a store with a custom callback.

Note

The callback must have two arguments: the store and the key.

Parameters:

• store – The store class to wrap.

• missing_key_callback (Callable) – Function(store, key) -> value for missing keys.

• errors_that_trigger_missing – Tuple of exceptions that trigger __missing__.

In the following example, we endow a store to return a sub-store when a key is missing. This substore will contain only keys that start with that missing key. This is useful, for example, to get “subfolder filtering” on a store.

>>> def prefix_filter(store, prefix: str):
...     '''Filter the store to have only keys that start with prefix'''
...     from dol import filt_iter
...     return filt_iter(store, filt=lambda x: x.startswith(prefix))
...
>>> @add_missing_key_handling(missing_key_callback=prefix_filter)
... class D(dict):
...     pass
>>>
>>> s = D({'a/b': 1, 'a/c': 2, 'd/e': 3, 'f': 4})
>>> sorted(s)
['a/b', 'a/c', 'd/e', 'f']
>>> 'a/' not in s
True
>>> # yet
>>> v = s['a/']
>>> assert dict(v) == {'a/b': 1, 'a/c': 2}

dol.trans.add_path_access(store=None, *, name=None, path_type=<class 'tuple'>, create_missing=False, mk_missing=None, explore_further=None, may_create=None, on_create=<function _warn_on_create>, max_created=None, max_levels=20, verify_writeback=False, writeback_lock=None, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Make nested stores (read/write) accessible through key paths (iterable of keys).

Like add_path_get, but with write and delete accessible through key paths.

In a way “flatten the nested keys access”. (Warning: path_type only effects the first level. That is, it doesn’t work recursively. See issue: https://github.com/i2mint/dol/issues/10.)

By default, the path object will be a tuple (e.g. ('a', 'b', 'c'), but you can make it whatever you want, and/or use dol.paths.KeyPath to map to and from forms like 'a.b.c', 'a/b/c', etc.

Say you have some nested stores. You know… like a ZipFileReader store whose values are ZipReader instances, whose values are bytes of the zipped files (and you can go on… whose (json) values are…).

For our example, let’s take a nested dict instead:

>>> s = {'a': {'b': {'c': 42}}}

Well, you can access any node of this nested tree of stores like this:

>>> s['a']['b']['c']
42

And that’s fine. But maybe you’d like to do it this way instead:

>>> s = add_path_access(s)
>>> s['a', 'b', 'c']
42

So far, this is what add_path_get does. With add_path_access though you can also write and delete that way too:

>>> s['a', 'b', 'c'] = 3.14
>>> s['a', 'b', 'c']
3.14
>>> del s['a', 'b', 'c']
>>> s
{'a': {'b': {}}}

You might also want to access 42 with a.b.c or a/b/c etc. To do that you can use dol.paths.KeyPath in combination with

Parameters:

• store – The store (class or instance) you’re wrapping. If not specified, the function will return a decorator.

• name – The name to give the class (not applicable to instance wrapping)

• path_type (type) – The type that paths are expressed as. Needs to be an Iterable type. By default, a tuple. This is used to decide whether the key should be taken as a “normal” key of the store, or should be used to iterate through, recursively getting values.

Returns:

A wrapped store (class or instance), or a store wrapping decorator (if store is not specified)

See also

KeyPath in dol.paths

Wrapping a class

>>> S = add_path_access(dict)
>>> s = S(a={'b': {'c': 42}})
>>> assert s['a'] == {'b': {'c': 42}};
>>> assert s['a', 'b'] == {'c': 42};
>>> assert s['a', 'b', 'c'] == 42
>>> s['a', 'b', 'c'] = 3.14
>>> s['a', 'b', 'c']
3.14
>>> del s['a', 'b', 'c']
>>> s
{'a': {'b': {}}}

Using add_path_get as a decorator

>>> @add_path_access
... class S(dict):
...    pass
>>> s = S(a={'b': {'c': 42}})
>>> assert s['a'] == {'b': {'c': 42}};
>>> assert s['a', 'b'] == s['a']['b'] == {'c': 42};
>>> assert s['a', 'b', 'c'] == s['a']['b']['c'] == 42
>>> s['a', 'b', 'c'] = 3.14
>>> s['a', 'b', 'c']
3.14
>>> del s['a', 'b', 'c']
>>> s
{'a': {'b': {}}}

A different kind of path? You can choose a different path_type, but sometimes (say both keys and key paths are strings) You need to involve more tools. Like dol.paths.KeyPath…

>>> from dol.paths import KeyPath
>>> from dol.trans import kv_wrap
>>> SS = kv_wrap(KeyPath(path_sep='.'))(S)
>>> s = SS({'a': {'b': {'c': 42}}})
>>> assert s['a'] == {'b': {'c': 42}};
>>> assert s['a.b'] == s['a']['b'];
>>> assert s['a.b.c'] == s['a']['b']['c']
>>> s['a.b.c'] = 3.14
>>> s
{'a': {'b': {'c': 3.14}}}
>>> del s['a.b.c']
>>> s
{'a': {'b': {}}}

Note

The add_path_access doesn’t carry on to values.

>>> s = add_path_access({'a': {'b': {'c': 42}}})
>>> s['a', 'b', 'c']
42
>>> # but
>>> s['a']['b', 'c']
Traceback (most recent call last):
  ...
KeyError: ('b', 'c')

That said,

>>> add_path_access(s['a'])['b', 'c']
42

The reason why we don’t do this automatically is that it may not always be desirable. If one wanted to though, one could use wrap_kvs(obj_of_data=...) to wrap specific values with add_path_access. For example, if you wanted to wrap all mappings recursively, you could:

>>> from typing import Mapping
>>> from dol.util import instance_checker
>>> add_path_access_if_mapping = conditional_data_trans(
...     condition=instance_checker(Mapping), data_trans=add_path_access
... )
>>> s = add_path_access_if_mapping({'a': {'b': {'c': 42}}})
>>> s['a', 'b', 'c']
42
>>> # But now this works:
>>> s['a']['b', 'c']
42

dol.trans.add_path_get(store=None, *, name=None, path_type=<class 'tuple'>, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Make nested stores accessible through key paths. In a way “flatten the nested keys access”. By default, the path object will be a tuple (e.g. ('a', 'b', 'c'), but you can make it whatever you want, and/or use dol.paths.KeyPath to map to and from forms like 'a.b.c', 'a/b/c', etc.

(Warning: path_type only effects the first level. That is, it doesn’t work recursively. See issue: https://github.com/i2mint/dol/issues/10.)

Say you have some nested stores. You know… like a ZipFileReader store whose values are ZipReader instances, whose values are bytes of the zipped files (and you can go on… whose (json) values are…).

For our example, let’s take a nested dict instead:

>>> s = {'a': {'b': {'c': 42}}}

Well, you can access any node of this nested tree of stores like this:

>>> s['a']['b']['c']
42

And that’s fine. But maybe you’d like to do it this way instead:

>>> s = add_path_get(s)
>>> s['a', 'b', 'c']
42

You might also want to access 42 with a.b.c or a/b/c etc. To do that you can use dol.paths.KeyPath in combination with

Parameters:

• store – The store (class or instance) you’re wrapping. If not specified, the function will return a decorator.

• name – The name to give the class (not applicable to instance wrapping)

• path_type (type) – The type that paths are expressed as. Needs to be an Iterable type. By default, a tuple. This is used to decide whether the key should be taken as a “normal” key of the store, or should be used to iterate through, recursively getting values.

Returns:

A wrapped store (class or instance), or a store wrapping decorator (if store is not specified)

See also

KeyPath in dol.paths

Wrapping an instance

>>> s = add_path_get({'a': {'b': {'c': 42}}})
>>> s['a']
{'b': {'c': 42}}
>>> s['a', 'b']
{'c': 42}
>>> s['a', 'b', 'c']
42

Wrapping a class

>>> S = add_path_get(dict)
>>> s = S(a={'b': {'c': 42}})
>>> assert s['a'] == {'b': {'c': 42}};
>>> assert s['a', 'b'] == {'c': 42};
>>> assert s['a', 'b', 'c'] == 42

Using add_path_get as a decorator

>>> @add_path_get
... class S(dict):
...    pass
>>> s = S(a={'b': {'c': 42}})
>>> assert s['a'] == {'b': {'c': 42}};
>>> assert s['a', 'b'] == s['a']['b'] == {'c': 42};
>>> assert s['a', 'b', 'c'] == s['a']['b']['c'] == 42

A different kind of path? You can choose a different path_type, but sometimes (say both keys and key paths are strings) You need to involve more tools. Like dol.paths.KeyPath…

>>> from dol.paths import KeyPath
>>> from dol.trans import kv_wrap
>>> SS = kv_wrap(KeyPath(path_sep='.'))(S)
>>> s = SS({'a': {'b': {'c': 42}}})
>>> assert s['a'] == {'b': {'c': 42}};
>>> assert s['a.b'] == s['a']['b'];
>>> assert s['a.b.c'] == s['a']['b']['c']

dol.trans.add_store_method(store, *, method_func, method_name=None, validator=None, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Add methods to store classes or instances

Parameters:

• store (type) – A store type or instance

• method_func – The function of the method to be added

• method_name – The name of the store attribute this function should be written to

• validator (Callable[[type, Callable], bool] | None) – An optional validator. If not None, validator(store, method_func) will be called. If it doesn’t return True, a SetattrNotAllowed will be raised. Note that validator can also raise its own exception.

Returns:

A store with the added (or modified) method

dol.trans.add_wrapper_method(wrap_cls=None, *, method_name='wrapper')

Decorator that adds a wrapper method (itself a decorator) to a wrapping class Clear? See mk_wrapper function and doctest example if not.

What add_wrapper_method does is just to add a "wrapper" method (or another name if you ask for it) to wrap_cls, so that you can use that class for it’s purpose of transforming stores more conveniently.

Parameters:

• wrap_cls – The wrapper class (the definitioin of the transformation. If None, the functiion will make a decorator to decorate wrap_cls later

• method_name – The method name you want to use (default is ‘wrapper’)

>>>
>>> @add_wrapper_method
... class RelPath:
...     def __init__(self, root):
...         self.root = root
...         self._root_length = len(root)
...     def _key_of_id(self, _id):
...         return _id[self._root_length:]
...     def _id_of_key(self, k):
...         return self.root + k
...
>>> RelDict = RelPath.wrapper(root='foo/')(dict)
>>> s = RelDict()
>>> s['bar'] = 42
>>> assert list(s) == ['bar']
>>> assert s['bar'] == 42
>>> assert str(s) == "{'foo/bar': 42}"  # reveals that actually, behind the scenes, there's a "foo/" prefix

dol.trans.affix_key_codec(prefix='', suffix='')

A factory that creates a key codec that affixes a prefix and suffix to the key

>>> codec = affix_key_codec(prefix='/folder/', suffix='.txt')
>>> codec.encoder('name')
'/folder/name.txt'
>>> codec.decoder('/folder/name.txt')
'name'

dol.trans.assert_min_num_of_args(func, num_of_args)

Assert that a function can be a store method. That is, it should have a signature that takes the store as the first argument

dol.trans.autoviv(store=None, **kwargs)

Opt-in write-through autovivification for key-paths.

Shorthand for add_path_access(store, create_missing=True, **kwargs): writing through a key-path (e.g. s['a', 'b', 'c'] = v) creates any missing intermediate levels on the way, and the change persists correctly even through persistent / copy-semantics stores (Files, wrap_kvs-wrapped stores). See add_path_access for the full set of options (mk_missing, may_create, max_created, on_create, …). Missing-key creation is announced via warnings.warn by default, so a typo is never silent.

>>> from dol import autoviv
>>> s = autoviv({})
>>> s['a', 'b', 'c'] = 42
>>> s['a', 'b', 'c']
42
>>> s['a']['b']['c']
42

Like add_path_access, it also works as a class decorator / factory:

>>> S = autoviv(dict)
>>> s = S()
>>> s['x', 'y'] = 1
>>> s['x', 'y']
1

dol.trans.cache_iter(store=None, *, keys_cache=<class 'list'>, iter_to_container=None, cache_update_method='update', name=None, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Make a class that wraps input class’s __iter__ becomes cached.

Quite often we have a lot of keys, that we get from a remote data source, and don’t want to have to ask for them again and again, having them be fetched, sent over the network, etc. So we need caching.

But this caching is not the typical read caching, since it’s __iter__ we want to cache, and that’s a generator. So we’ll implement a store class decorator specialized for this.

The following decorator, when applied to a class (that has an __iter__), will perform the __iter__ code, consuming all items of the generator and storing them in _keys_cache, and then will yield from there every subsequent call.

It is assumed, if you’re using the cached_keys transformation, that you’re dealing with static data (or data that can be considered static for the life of the store – for example, when conducting analytics). If you ever need to refresh the cache during the life of the store, you can to delete _keys_cache like this:

del your_store._keys_cache

Once you do that, the next time you try to ask something about the contents of the store, it will actually do a live query again, as for the first time.

Note

The default keys_cache is list though in many cases, you’d probably should use set, or an explicitly computer set instead. The reason list is used as the default is because (1) we didn’t want to assume that order did not matter (maybe it does to you) and (2) we didn’t want to assume that your keys were hashable. That said, if you’re keys are hashable, and order does not matter, use set. That’ll give you two things: (a) your key in store checks will be faster (O(1) instead of O(n)) and (b) you’ll enforce unicity of keys.

Know also that if you precompute the keys you want to cache with a container that has an update method (by default update) your cache updates will be faster and if the container you use has a remove method, you’ll be able to delete as well.

Parameters:

• store – The store instance or class to wrap (must have an __iter__), or None if you want a decorator.

• keys_cache (Callable | Collection) – An explicit collection of keys

• iter_to_container – The function that will be applied to existing __iter__() and assigned to cache. The default is list. Another useful one is the sorted function.

• cache_update_method – Name of the keys_cache update method to use, if it is an attribute of keys_cache (whether keys_cache is an explicit iterable or a callable). Default 'update'.

• name (str) – The name of the new class

Return type:

Callable | KvReader

Returns:

If store is None, a decorator that can be applied to a store; if store is a class, a wrapped class that caches its keys; if store is an instance, a wrapped instance that caches its keys.

The instances of such key-cached classes have some extra attributes: _keys_cache (the actual cache), _explicit_keys (whether the cache was given explicitly) and update_keys_cache (called on __setitem__ and update).

You have two ways of caching keys:

• By providing the explicit list of keys you want cache (and use)

• By providing a callable that will iterate through your store and collect an explicit list of keys

Let’s take a simple dict as our original store.

>>> source = dict(c=3, b=2, a=1)

Specify an iterable, and it will be used as the cached keys

>>> cached = cached_keys(source, keys_cache='bc')
>>> list(cached.items())  # notice that the order you get things is also ruled by the cache
[('b', 2), ('c', 3)]

Specify a callable, and it will apply it to the existing keys to make your cache

>>> list(cached_keys(source, keys_cache=sorted))
['a', 'b', 'c']

You can use the callable keys_cache specification to filter as well! Oh, and let’s demo the fact that if you don’t specify the store, it will make a store decorator for you:

>>> cache_my_keys = cached_keys(keys_cache=lambda keys: list(filter(lambda k: k >= 'b', keys)))
>>> d = cache_my_keys(source)  # used as to transform an instance
>>> list(d)
['c', 'b']

Let’s use that same cache_my_keys to decorate a class instead:

>>> cached_dict = cache_my_keys(dict)
>>> d = cached_dict(c=3, b=2, a=1)
>>> list(d)
['c', 'b']

Note that there’s still an underlying store (dict) that has the data:

>>> repr(d)  # repr isn't wrapped, so you can still see your underlying dict
"{'c': 3, 'b': 2, 'a': 1}"

And yes, you can still add elements,

>>> d['z'] = 26
>>> list(d.items())
[('c', 3), ('b', 2), ('z', 26)]

do bulk updates,

>>> d.update({'more': 'of this'}, more_of='that')
>>> list(d.items())
[('c', 3), ('b', 2), ('z', 26), ('more', 'of this'), ('more_of', 'that')]

and delete…

>>> del d['more']
>>> list(d.items())
[('c', 3), ('b', 2), ('z', 26), ('more_of', 'that')]

But careful! Know what you’re doing if you try to get creative. Have a look at this:

>>> d['a'] = 100  # add an 'a' item
>>> d.update(and_more='of that')  # update to add yet another item
>>> list(d.items())
[('c', 3), ('b', 2), ('z', 26), ('more_of', 'that')]

Indeed: No ‘a’ or ‘and_more’.

Now… they were indeed added. Or to be more precise, the value of the already existing a was changed, and a new (‘and_more’, ‘of that’) item was indeed added in the underlying store:

>>> repr(d)
"{'c': 3, 'b': 2, 'a': 100, 'z': 26, 'more_of': 'that', 'and_more': 'of that'}"

But you’re not seeing it.

Why?

Because you chose to use a callable keys_cache that doesn’t have an ‘update’ method. When your _keys_cache attribute (the iterable cache) is not updatable itself, the way updates work is that we iterate through the underlying store (where the updates actually took place), and apply the keys_cache (callable) to that iterable.

So what happened here was that you have your new ‘a’ and ‘and_more’ items, but your cached version of the store doesn’t see it because it’s filtered out. On the other hand, check out what happens if you have an updateable cache.

Using set instead of list, after the filter.

>>> cache_my_keys = cached_keys(keys_cache=set)
>>> d = cache_my_keys(source)  # used as to transform an instance
>>> sorted(d)  # using sorted because a set's order is not always the same
['a', 'b', 'c']
>>> d['a'] = 100
>>> d.update(and_more='of that')  # update to add yet another item
>>> sorted(d.items())
[('a', 100), ('and_more', 'of that'), ('b', 2), ('c', 3)]

This example was to illustrate a more subtle aspect of cached_keys. You would probably deal with the filter concern in a different way in this case. But the rope is there – it’s your choice on how to use it.

And here’s some more examples if that wasn’t enough!

>>> # Lets cache the keys of a dict.
>>> cached_dict = cached_keys(dict)
>>> d = cached_dict(a=1, b=2, c=3)
>>> # And you get a store that behaves as expected (but more speed and RAM)
>>> list(d)
['a', 'b', 'c']
>>> list(d.items())  # whether you iterate with .keys(), .values(), or .items()
[('a', 1), ('b', 2), ('c', 3)]

This is where the keys are stored:

>>> d._keys_cache
['a', 'b', 'c']

>>> # Let's demo the iter_to_container argument. The default is "list", which will just consume the iter in order
>>> sorted_dict = cached_keys(dict, keys_cache=list)
>>> s = sorted_dict({'b': 3, 'a': 2, 'c': 1})
>>> list(s)  # keys will be in the order they were defined
['b', 'a', 'c']
>>> sorted_dict = cached_keys(dict, keys_cache=sorted)
>>> s = sorted_dict({'b': 3, 'a': 2, 'c': 1})
>>> list(s)  # keys will be sorted
['a', 'b', 'c']
>>> sorted_dict = cached_keys(dict, keys_cache=lambda x: sorted(x, key=len))
>>> s = sorted_dict({'bbb': 3, 'aa': 2, 'c': 1})
>>> list(s)  # keys will be sorted according to their length
['c', 'aa', 'bbb']

If you change the keys (adding new ones with __setitem__ or update, or removing with pop or popitem) then the cache is recomputed (the first time you use an operation that iterates over keys)

>>> d.update(d=4)  # let's add an element (try d['d'] = 4 as well)
>>> list(d)
['a', 'b', 'c', 'd']
>>> d['e'] = 5
>>> list(d.items())  # whether you iterate with .keys(), .values(), or .items()
[('a', 1), ('b', 2), ('c', 3), ('d', 4), ('e', 5)]

>>> @cached_keys
... class A:
...     def __iter__(self):
...         yield from [1, 2, 3]
>>> # Note, could have also used this form: AA = cached_keys(A)
>>> a = A()
>>> list(a)
[1, 2, 3]
>>> a._keys_cache = ['a', 'b', 'c']  # changing the cache, to prove that subsequent listing will read from there
>>> list(a)  # proof:
['a', 'b', 'c']
>>>

>>> # Let's demo the iter_to_container argument. The default is "list", which will just consume the iter in order
>>> sorted_dict = cached_keys(dict, keys_cache=list)
>>> s = sorted_dict({'b': 3, 'a': 2, 'c': 1})
>>> list(s)  # keys will be in the order they were defined
['b', 'a', 'c']
>>> sorted_dict = cached_keys(dict, keys_cache=sorted)
>>> s = sorted_dict({'b': 3, 'a': 2, 'c': 1})
>>> list(s)  # keys will be sorted
['a', 'b', 'c']
>>> sorted_dict = cached_keys(dict, keys_cache=lambda x: sorted(x, key=len))
>>> s = sorted_dict({'bbb': 3, 'aa': 2, 'c': 1})
>>> list(s)  # keys will be sorted according to their length
['c', 'aa', 'bbb']

dol.trans.cached_keys(store=None, *, keys_cache=<class 'list'>, iter_to_container=None, cache_update_method='update', name=None, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Make a class that wraps input class’s __iter__ becomes cached.

Quite often we have a lot of keys, that we get from a remote data source, and don’t want to have to ask for them again and again, having them be fetched, sent over the network, etc. So we need caching.

But this caching is not the typical read caching, since it’s __iter__ we want to cache, and that’s a generator. So we’ll implement a store class decorator specialized for this.

The following decorator, when applied to a class (that has an __iter__), will perform the __iter__ code, consuming all items of the generator and storing them in _keys_cache, and then will yield from there every subsequent call.

It is assumed, if you’re using the cached_keys transformation, that you’re dealing with static data (or data that can be considered static for the life of the store – for example, when conducting analytics). If you ever need to refresh the cache during the life of the store, you can to delete _keys_cache like this:

del your_store._keys_cache

Once you do that, the next time you try to ask something about the contents of the store, it will actually do a live query again, as for the first time.

Note

The default keys_cache is list though in many cases, you’d probably should use set, or an explicitly computer set instead. The reason list is used as the default is because (1) we didn’t want to assume that order did not matter (maybe it does to you) and (2) we didn’t want to assume that your keys were hashable. That said, if you’re keys are hashable, and order does not matter, use set. That’ll give you two things: (a) your key in store checks will be faster (O(1) instead of O(n)) and (b) you’ll enforce unicity of keys.

Know also that if you precompute the keys you want to cache with a container that has an update method (by default update) your cache updates will be faster and if the container you use has a remove method, you’ll be able to delete as well.

Parameters:

• store – The store instance or class to wrap (must have an __iter__), or None if you want a decorator.

• keys_cache (Callable | Collection) – An explicit collection of keys

• iter_to_container – The function that will be applied to existing __iter__() and assigned to cache. The default is list. Another useful one is the sorted function.

• cache_update_method – Name of the keys_cache update method to use, if it is an attribute of keys_cache (whether keys_cache is an explicit iterable or a callable). Default 'update'.

• name (str) – The name of the new class

Return type:

Callable | KvReader

Returns:

If store is None, a decorator that can be applied to a store; if store is a class, a wrapped class that caches its keys; if store is an instance, a wrapped instance that caches its keys.

The instances of such key-cached classes have some extra attributes: _keys_cache (the actual cache), _explicit_keys (whether the cache was given explicitly) and update_keys_cache (called on __setitem__ and update).

You have two ways of caching keys:

• By providing the explicit list of keys you want cache (and use)

• By providing a callable that will iterate through your store and collect an explicit list of keys

Let’s take a simple dict as our original store.

>>> source = dict(c=3, b=2, a=1)

Specify an iterable, and it will be used as the cached keys

>>> cached = cached_keys(source, keys_cache='bc')
>>> list(cached.items())  # notice that the order you get things is also ruled by the cache
[('b', 2), ('c', 3)]

Specify a callable, and it will apply it to the existing keys to make your cache

>>> list(cached_keys(source, keys_cache=sorted))
['a', 'b', 'c']

You can use the callable keys_cache specification to filter as well! Oh, and let’s demo the fact that if you don’t specify the store, it will make a store decorator for you:

>>> cache_my_keys = cached_keys(keys_cache=lambda keys: list(filter(lambda k: k >= 'b', keys)))
>>> d = cache_my_keys(source)  # used as to transform an instance
>>> list(d)
['c', 'b']

Let’s use that same cache_my_keys to decorate a class instead:

>>> cached_dict = cache_my_keys(dict)
>>> d = cached_dict(c=3, b=2, a=1)
>>> list(d)
['c', 'b']

Note that there’s still an underlying store (dict) that has the data:

>>> repr(d)  # repr isn't wrapped, so you can still see your underlying dict
"{'c': 3, 'b': 2, 'a': 1}"

And yes, you can still add elements,

>>> d['z'] = 26
>>> list(d.items())
[('c', 3), ('b', 2), ('z', 26)]

do bulk updates,

>>> d.update({'more': 'of this'}, more_of='that')
>>> list(d.items())
[('c', 3), ('b', 2), ('z', 26), ('more', 'of this'), ('more_of', 'that')]

and delete…

>>> del d['more']
>>> list(d.items())
[('c', 3), ('b', 2), ('z', 26), ('more_of', 'that')]

But careful! Know what you’re doing if you try to get creative. Have a look at this:

>>> d['a'] = 100  # add an 'a' item
>>> d.update(and_more='of that')  # update to add yet another item
>>> list(d.items())
[('c', 3), ('b', 2), ('z', 26), ('more_of', 'that')]

Indeed: No ‘a’ or ‘and_more’.

Now… they were indeed added. Or to be more precise, the value of the already existing a was changed, and a new (‘and_more’, ‘of that’) item was indeed added in the underlying store:

>>> repr(d)
"{'c': 3, 'b': 2, 'a': 100, 'z': 26, 'more_of': 'that', 'and_more': 'of that'}"

But you’re not seeing it.

Why?

Because you chose to use a callable keys_cache that doesn’t have an ‘update’ method. When your _keys_cache attribute (the iterable cache) is not updatable itself, the way updates work is that we iterate through the underlying store (where the updates actually took place), and apply the keys_cache (callable) to that iterable.

So what happened here was that you have your new ‘a’ and ‘and_more’ items, but your cached version of the store doesn’t see it because it’s filtered out. On the other hand, check out what happens if you have an updateable cache.

Using set instead of list, after the filter.

>>> cache_my_keys = cached_keys(keys_cache=set)
>>> d = cache_my_keys(source)  # used as to transform an instance
>>> sorted(d)  # using sorted because a set's order is not always the same
['a', 'b', 'c']
>>> d['a'] = 100
>>> d.update(and_more='of that')  # update to add yet another item
>>> sorted(d.items())
[('a', 100), ('and_more', 'of that'), ('b', 2), ('c', 3)]

This example was to illustrate a more subtle aspect of cached_keys. You would probably deal with the filter concern in a different way in this case. But the rope is there – it’s your choice on how to use it.

And here’s some more examples if that wasn’t enough!

>>> # Lets cache the keys of a dict.
>>> cached_dict = cached_keys(dict)
>>> d = cached_dict(a=1, b=2, c=3)
>>> # And you get a store that behaves as expected (but more speed and RAM)
>>> list(d)
['a', 'b', 'c']
>>> list(d.items())  # whether you iterate with .keys(), .values(), or .items()
[('a', 1), ('b', 2), ('c', 3)]

This is where the keys are stored:

>>> d._keys_cache
['a', 'b', 'c']

>>> # Let's demo the iter_to_container argument. The default is "list", which will just consume the iter in order
>>> sorted_dict = cached_keys(dict, keys_cache=list)
>>> s = sorted_dict({'b': 3, 'a': 2, 'c': 1})
>>> list(s)  # keys will be in the order they were defined
['b', 'a', 'c']
>>> sorted_dict = cached_keys(dict, keys_cache=sorted)
>>> s = sorted_dict({'b': 3, 'a': 2, 'c': 1})
>>> list(s)  # keys will be sorted
['a', 'b', 'c']
>>> sorted_dict = cached_keys(dict, keys_cache=lambda x: sorted(x, key=len))
>>> s = sorted_dict({'bbb': 3, 'aa': 2, 'c': 1})
>>> list(s)  # keys will be sorted according to their length
['c', 'aa', 'bbb']

If you change the keys (adding new ones with __setitem__ or update, or removing with pop or popitem) then the cache is recomputed (the first time you use an operation that iterates over keys)

>>> d.update(d=4)  # let's add an element (try d['d'] = 4 as well)
>>> list(d)
['a', 'b', 'c', 'd']
>>> d['e'] = 5
>>> list(d.items())  # whether you iterate with .keys(), .values(), or .items()
[('a', 1), ('b', 2), ('c', 3), ('d', 4), ('e', 5)]

>>> @cached_keys
... class A:
...     def __iter__(self):
...         yield from [1, 2, 3]
>>> # Note, could have also used this form: AA = cached_keys(A)
>>> a = A()
>>> list(a)
[1, 2, 3]
>>> a._keys_cache = ['a', 'b', 'c']  # changing the cache, to prove that subsequent listing will read from there
>>> list(a)  # proof:
['a', 'b', 'c']
>>>

>>> # Let's demo the iter_to_container argument. The default is "list", which will just consume the iter in order
>>> sorted_dict = cached_keys(dict, keys_cache=list)
>>> s = sorted_dict({'b': 3, 'a': 2, 'c': 1})
>>> list(s)  # keys will be in the order they were defined
['b', 'a', 'c']
>>> sorted_dict = cached_keys(dict, keys_cache=sorted)
>>> s = sorted_dict({'b': 3, 'a': 2, 'c': 1})
>>> list(s)  # keys will be sorted
['a', 'b', 'c']
>>> sorted_dict = cached_keys(dict, keys_cache=lambda x: sorted(x, key=len))
>>> s = sorted_dict({'bbb': 3, 'aa': 2, 'c': 1})
>>> list(s)  # keys will be sorted according to their length
['c', 'aa', 'bbb']

dol.trans.catch_and_cache_error_keys(store=None, *, errors_caught=<class 'Exception'>, error_callback=None, use_cached_keys_after_completed_iter=True, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Store that will cache keys as they’re accessed, separating those that raised errors and those that didn’t. Getting a key will still through an error, but the access attempts will be collected in an ._error_keys attribute. Successfful attemps will be stored in _keys_cache. Retrieval iteration (items() or values()) will on the other hand, skip the error (while still caching it). If the iteration completes (and use_cached_keys_after_completed_iter), the use_cached_keys flag is turned on, which will result in the store now getting it’s keys from the _keys_cache.

>>> @catch_and_cache_error_keys(
...     error_callback=lambda store, key, err: print(f"Error with {key} key: {err}"))
... class Blacklist(dict):
...     _black_list = {'black', 'list'}
...
...     def __getitem__(self, k):
...         if k not in self._black_list:
...             return super().__getitem__(k)
...         else:
...             raise KeyError(f"Nope, that's from the black list!")
>>>
>>> s = Blacklist(black=7,  friday=20, frenzy=13)
>>> list(s)
['black', 'friday', 'frenzy']
>>> list(s.items())
Error with black key: "Nope, that's from the black list!"
[('friday', 20), ('frenzy', 13)]
>>> sorted(s)  # sorting to get consistent output
['frenzy', 'friday']

See that? First we had three keys, then we iterated and got only 2 items (fortunately, we specified an error_callback so we ccould see that the iteration actually dropped a key).

That’s strange. And even stranger is the fact that when we list our keys again, we get only two.

You don’t like it? Neither do I. But

• It’s not a completely outrageous behavior – if you’re talking to live data, it often happens that you get more, or less, from one second to another.

• This store isn’t meant to be long living, but rather meant to solve the problem of skiping items that are problematic (for example, malformatted files), with a trace of what was skipped and what’s valid (in case we need to iterate again and don’t want to bear the hit of requesting values for keys we already know are problematic.

Here’s a little peep of what is happening under the hood. Meet _keys_cache and _error_keys sets (yes, unordered – so know it) that are meant to acccumulate valid and problematic keys respectively.

>>> s = Blacklist(black=7,  friday=20, frenzy=13)
>>> list(s)
['black', 'friday', 'frenzy']
>>> s._keys_cache, s._error_keys
(set(), set())
>>> s['friday']
20
>>> s._keys_cache, s._error_keys
({'friday'}, set())
>>> s['black']
Traceback (most recent call last):
  ...
KeyError: "Nope, that's from the black list!"
>>> s._keys_cache, s._error_keys
({'friday'}, {'black'})

But see that we still have the full list:

>>> list(s)
['black', 'friday', 'frenzy']

Meet use_cached_keys: He’s the culprit. It’s a flag that indicates whether we should be using the cached keys or not. Obviously, it’ll start off being False:

>>> s.use_cached_keys
False

Now we could set it to True manually to change the mode. But know that this switch happens automatically (UNLESS you specify otherwise by saying:use_cached_keys_after_completed_iter=False) when ever you got through a VALUE-PRODUCING iteration (i.e. entirely consuming items() or values()).

>>> sorted(s.values())  # sorting to get consistent output
Error with black key: "Nope, that's from the black list!"
[13, 20]

dol.trans.condition_function_call(func=None, *, condition=functools.partial(<function constant_output>, True), callback_if_condition_not_met=functools.partial(<function constant_output>, None))

Decorator: call func only when condition(*args, **kwargs) holds, else callback_if_condition_not_met.

dol.trans.conditional_data_trans(store=None, *, condition, data_trans, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Wrap store so that data_trans is applied to the read values satisfying condition (others pass through).

dol.trans.confirm_overwrite(self, k, v)

A ready-to-use wrap_kvs preset that asks (via the builtin input) to confirm before overwriting an existing key with a different value (Issue #13). For customization (e.g. a non-interactive confirmation policy), use mk_confirm_overwrite_preset().

>>> from dol import wrap_kvs, confirm_overwrite
>>> d = wrap_kvs(dict(a='apple', b='banana'), preset=confirm_overwrite)
>>> d['a'] = 'apple'      # same value -> no prompt, no change
>>> d['c'] = 'coconut'    # new key   -> no prompt, written
>>> dict(d) == {'a': 'apple', 'b': 'banana', 'c': 'coconut'}
True

dol.trans.constant_output(return_val=None, *args, **kwargs)

Function that returns a constant value no matter what the inputs are. Is meant to be used with functools.partial to create custom versions.

>>> from functools import partial
>>> always_true = partial(constant_output, True)
>>> always_true('regardless', 'of', the='input', will='return True')
True

dol.trans.disable_delitem(o)

Replace o.__delitem__ (if any) with a function raising ValueError.

Meant for classes: on an instance, del o[k] still uses the type’s method.

dol.trans.disable_setitem(o)

Replace o.__setitem__ (if any) with a function raising ValueError.

Meant for classes: on an instance, o[k] = v still uses the type’s method.

dol.trans.disallow_overwrites(store, *, error_msg=None, disable_deletes=True)

Return a subclass of store whose __setitem__ raises OverWritesNotAllowedError on existing keys (store itself is left untouched).

Parameters:

• store – The store class to wrap (must be a type).

• error_msg – Custom error message; {} (or {k}) in it is filled in with the offending key via .format. Defaults to a generic message.

• disable_deletes – If True (the default), also disable __delitem__ (raising the same error) – since deleting a key and rewriting it would otherwise be a way around the overwrite guard.

Returns:

A new subclass of store with the guard(s) attached.

>>> class D(dict): ...
>>> ND = disallow_overwrites(D)
>>> d = ND(a=1)
>>> d['b'] = 2
>>> d['a'] = 1
Traceback (most recent call last):
  ...
dol.errors.OverWritesNotAllowedError: key a already exists and cannot be overwritten...
>>> del d['a']
Traceback (most recent call last):
  ...
dol.errors.OverWritesNotAllowedError: delete of key a is not allowed

With disable_deletes=False, deletes are left alone:

>>> ND2 = disallow_overwrites(D, disable_deletes=False)
>>> d2 = ND2(a=1)
>>> del d2['a']  # no error
>>> d2['a'] = 2  # no error either, since 'a' was deleted first

dol.trans.double_up_as_factory(decorator_func)

Repurpose a decorator both as it’s original form, and as a decorator factory. That is, from a decorator that is defined do wrapped_func = decorator(func, **params), make it also be able to do wrapped_func = decorator(**params)(func).

Note

You’ll only be able to do this if all but the first argument are keyword-only, and the first argument (the function to decorate) has a default of None (this is for your own good). This is validated before making the “double up as factory” decorator.

>>> @double_up_as_factory
... def decorator(func=None, *, multiplier=2):
...     def _func(x):
...         return func(x) * multiplier
...     return _func
...
>>> def foo(x):
...     return x + 1
...
>>> foo(2)
3
>>> wrapped_foo = decorator(foo, multiplier=10)
>>> wrapped_foo(2)
30
>>>
>>> multiply_by_3 = decorator(multiplier=3)
>>> wrapped_foo = multiply_by_3(foo)
>>> wrapped_foo(2)
9
>>>
>>> @decorator(multiplier=3)
... def foo(x):
...     return x + 1
...
>>> foo(2)
9

Note that to be able to use double_up_as_factory, your first argument (the object to be wrapped) needs to default to None and be the only argument that is not keyword-only (i.e. all other arguments need to be keyword only).

>>> @double_up_as_factory
... def decorator_2(func, *, multiplier=2):
...     '''Should not be able to be transformed with double_up_as_factory'''
Traceback (most recent call last):
  ...
AssertionError: First argument of the decorator function needs to default to None. Was <class 'inspect._empty'>
>>> @double_up_as_factory
... def decorator_3(func=None, multiplier=2):
...     '''Should not be able to be transformed with double_up_as_factory'''
Traceback (most recent call last):
  ...
AssertionError: All arguments (besides the first) need to be keyword-only

dol.trans.ensure_clear_method(store=None, *, clear_method=<function _delete_keys_one_by_one>)

If obj doesn’t have an enabled clear method, will add one (a slow one that runs through keys and deletes them

dol.trans.ensure_set(x)

A set from x, treating a string as a single element.

dol.trans.filt_iter(store=None, *, filt=<function take_everything>, name=None, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Make a wrapper that will transform a store (class or instance thereof) into a sub-store (i.e. subset of keys).

Parameters:

• filt (Callable | Iterable) – A callable or iterable. If a callable, a boolean filter function taking a key and returning True iff the key should be included. If an iterable, the collection of keys you want to filter “in”.

• name – The name to give the wrapped class

Returns:

A wrapper (that then needs to be applied to a store instance or class.

>>> filtered_dict = filt_iter(filt=lambda k: (len(k) % 2) == 1)(dict)  # keep only odd length keys
>>>
>>> s = filtered_dict({'a': 1, 'bb': object, 'ccc': 'a string', 'dddd': [1, 2]})
>>>
>>> list(s)
['a', 'ccc']
>>> 'a' in s  # True because odd (length) key
True
>>> 'bb' in s  # False because odd (length) key
False
>>> assert s.get('bb', None) == None
>>> len(s)
2
>>> list(s.keys())
['a', 'ccc']
>>> list(s.values())
[1, 'a string']
>>> list(s.items())
[('a', 1), ('ccc', 'a string')]
>>> s.get('a')
1
>>> assert s.get('bb') is None
>>> s['x'] = 10
>>> list(s.items())
[('a', 1), ('ccc', 'a string'), ('x', 10)]
>>> try:
...     s['xx'] = 'not an odd key'
...     raise ValueError("This should have failed")
... except KeyError:
...     pass

dol.trans.filter_prefixes(prefixes)

Make a filter that returns True if a string starts with one of the given prefixes

>>> starts_with_test = filter_prefixes('test')
>>> starts_with_test("test.txt")
True
>>> starts_with_test("report.doc")
False
>>> is_test_or_report = filter_prefixes(['test', 'report'])
>>> is_test_or_report("test.txt")
True
>>> is_test_or_report("report.doc")
True
>>> is_test_or_report("image.jpg")
False

The prefixes are grouped, so a multi-prefix filter doesn’t accidentally match a string that merely contains one of the later prefixes anywhere:

>>> is_logs_or_tmp = filter_prefixes(['logs/', 'tmp/'])
>>> is_logs_or_tmp("other/tmp/c")
False

dol.trans.filter_regex(regex, *, return_search_func=False)

Make a filter that returns True if a string matches the given regex

>>> is_txt = filter_regex(r'.*\.txt')
>>> is_txt("test.txt")
True
>>> is_txt("report.doc")
False

The argument is a regular expression, so it is compiled with re.compile – NOT safe_compile (which is for file-path templates and re.escape``s its input on Windows). Using ``safe_compile here silently broke every regex filter on Windows: e.g. filter_suffixes('.json') (used by Jsons) had its (\.json)$ pattern escaped into a literal string matcher, so no *.json key matched and the store raised KeyError: 'Key not in store: <key>.json'.

>>> is_json = filter_regex(r"(\.json)$")  # works identically on every OS
>>> is_json("doc-001.json")
True
>>> is_json("doc-001.txt")
False

dol.trans.filter_suffixes(suffixes)

Make a filter that returns True if a string ends with one of the given suffixes

>>> ends_with_txt = filter_suffixes('.txt')
>>> ends_with_txt("test.txt")
True
>>> ends_with_txt("report.doc")
False
>>> is_text = filter_suffixes(['.txt', '.doc', '.pdf'])
>>> is_text("test.txt")
True
>>> is_text("report.doc")
True
>>> is_text("image.jpg")
False

dol.trans.flatten(store=None, *, levels=None, cache_keys=False, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Give a nested store a flat view whose keys are the (a, b, c) key paths.

Say you have a store that has three levels (or more), that is, that you can always ask for the value store[a][b][c] if a is a valid key of store, b is a valid key of store[a] and c is a valid key of store[a][b].

What flattened_store = flatten(store, levels=3) will give you is the ability to access the store[a][b][c] as store[a, b, c], while still being able to access these stores “normally”.

If that’s all you need, you can just use the add_get_path wrapper for this.

Why would you use flatten? Because add_get_path(store) would still only give you the KvReader point of view of the root store. If you list(store), you’d only get the first level keys, or if you ask if (a, b, c) is in the store, it will tell you it’s not (though you can access data with such a key.

Instead, a flattened store will consider that the keys are those (a, b, c) key paths.

Further, when flattening a store, you can ask for the view to cache the keys, specifying cache_keys=True or give it an explicit place to cache or factory to make a cache (see cached_keys wrapper for more details). Though caching keys is not the default it’s highly recommended to do so in most cases. The only reason it is not the default is because if you have millions of keys, but little memory, that’s not what you might want.

Note

Flattening just provides a wrapper giving you a “flattened view”. It doesn’t change the store itself, or it’s contents.

Parameters:

• store – The store instance or class to be wrapped

• levels – The number of nested levels to flatten

• cache_keys – Whether to cache the keys, or a cache factory or instance.

>>> from dol import flatten
>>> d = {
...     'a': {'b': {'c': 42}},
...     'aa': {'bb': {'cc': 'dragon_con'}}
... }

You can get a flattened view of an instance:

>>> m = flatten(d, levels=3, cache_keys=True)
>>> assert (
...         list(m.items())
...         == [
...             (('a', 'b', 'c'), 42),
...             (('aa', 'bb', 'cc'), 'dragon_con')
...         ]
... )

You can make a flattener and apply it to an instance (or a class):

>>> my_flattener = flatten(levels=2)
>>> m = my_flattener(d)
>>> assert (
...         list(m.items())
...         == [
...             (('a', 'b'), {'c': 42}),
...             (('aa', 'bb'), {'cc': 'dragon_con'})
...         ]
... )

Finally, you can wrap a class itself.

>>> @flatten(levels=1)
... class MyFlatDict(dict):
...     pass
>>> m = MyFlatDict(d)
>>> assert (
...         list(m.items())
...         == [
...             (('a',), {'b': {'c': 42}}),
...             (('aa',), {'bb': {'cc': 'dragon_con'}})
...         ]
... )

dol.trans.get_class_name(cls, dflt_name=None)

The __qualname__ of cls (or of its class), else dflt_name; raises ValueError if there is neither.

dol.trans.ignore_if_error(store=None, *, errors=(<class 'KeyError'>, ))

Wrap store so that __getitem__ errors in errors return None instead of raising.

dol.trans.insert_aliases(store=None, *, write=None, read=None, delete=None, list=None, count=None, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Insert method aliases of CRUD operations of a store (class or instance). If store is a class, you’ll get a copy of the class with those methods added. If store is an instance, the methods will be added in place (no copy will be made).

Note

If an operation (write, read, delete, list, count) is not specified, no alias will be created for that operation.

IMPORTANT NOTE: The signatures of the methods the aliases will point to will not change. We say this because, you can call the write method “dump”, but you’ll have to use it as store.dump(key, val), not store.dump(val, key), which is the signature you’re probably used to (it’s the one used by json.dump or pickle.dump for example). If you want that familiar interface, using the insert_load_dump_aliases function.

See also (and not to be confused with): add_aliases

Parameters:

• store – The store to extend with aliases.

• write – Desired method name for __setitem__

• read – Desired method name for __getitem__

• delete – Desired method name for __delitem__

• list – Desired method name for __iter__

• count – Desired method name for __len__

Returns:

A store with the desired aliases.

>>> # Example of extending a class
>>> mydict = insert_aliases(dict, write='dump', read='load', delete='rm', list='peek', count='size')
>>> s = mydict(true='love')
>>> s.dump('friends', 'forever')
>>> s
{'true': 'love', 'friends': 'forever'}
>>> s.load('true')
'love'
>>> list(s.peek())
['true', 'friends']
>>> s.size()
2
>>> s.rm('true')
>>> s
{'friends': 'forever'}
>>>
>>> # Example of extending an instance
>>> from collections import UserDict
>>> s = UserDict(true='love')  # make (and instance) of a UserDict (can't modify a dict instance)
>>> # make aliases of note that you don't need
>>> s = insert_aliases(s, write='put', read='retrieve', count='num_of_items')
>>> s.put('friends', 'forever')
>>> s
{'true': 'love', 'friends': 'forever'}
>>> s.retrieve('true')
'love'
>>> s.num_of_items()
2

dol.trans.insert_hash_method(store=None, *, hash_method=<built-in function id>, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Make a store hashable using the specified hash_method. Will add (or overwrite) a __hash__ method to the store that uses the hash_method to hash the store and an __eq__ method that compares the store to another based on the hash_method.

The hash_method, which will be used as the __hash__ method of a class should return an integer value that represents the hash of the object. To remain sane, the hash value must be the same for an object every time the __hash__ method is called during the lifetime of the object, and objects that compare equal (using the __eq__ method) must have the same hash value.

It’s also important that the hash function has the property of being deterministic and returning a hash value that is uniformly distributed across the range of possible integers for the given data. This is important for the hash table data structure to work efficiently.

See This issue for further information.

>>> d = {1: 2}  # not hashable!
>>> dd = insert_hash_method(d)
>>> assert isinstance(hash(dd), int)  # now hashable!

It looks the same:

>>> dd
{1: 2}

But don’t be fooled: dd is not equal to the original d (since insert_hash_method``overwrote the __eq__ method to compare based on the hash value):

>>> d == dd
False

But if you cast both to dicts and then compare, you’ll be using the key and value based comparison of dicts, which makes these two equal.

>>> dict(d) == dict(dd)
True

The default hash_method is id, so two hashable wrappers won’t be equal to eachother:

>>> insert_hash_method(d) == insert_hash_method(d)
False

In the following we show two things: That you can specify your own custom hash_method, and that you can use insert_hash_method to wrap classes

>>> class D(dict):
...     pass
>>> DD = insert_hash_method(D, hash_method=lambda x: 42)
>>> hash(DD(d))
42

You can also use it as a decorator, without arguments,

>>> @insert_hash_method
... class E(dict):
...     pass
>>> assert isinstance(hash(E({1: 2})), int)

or with arguments (which you must specify as keyword arguments):

>>> @insert_hash_method(hash_method=lambda x: sum(x.values()))
... class F(dict):
...     pass
>>> hash(F({1: 2, 3: 4}))
6

dol.trans.insert_load_dump_aliases(store=None, *, delete=None, list=None, count=None, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Insert load and dump methods, with familiar dump(obj, location) signature.

Parameters:

• store – The store to extend with aliases.

• delete – Desired method name for __delitem__

• list – Desired method name for __iter__

• count – Desired method name for __len__

Returns:

A store with the desired aliases.

>>> mydict = insert_load_dump_aliases(dict)
>>> s = mydict()
>>> s.dump(obj='love', key='true')
>>> s
{'true': 'love'}

dol.trans.is_iterable(x)

Whether x is an Iterable.

dol.trans.iterate_values_and_accumulate_non_error_keys(store, cache_keys_here, errors_caught=<class 'Exception'>, error_callback=None)

Yield the values of store, appending to cache_keys_here the keys whose value was fetched without error.

dol.trans.kv_wrap(trans_obj)

A function that makes a wrapper (a decorator) that will get the wrappers from methods of the input object.

Parameters:

trans_obj – An object that contains (as attributes) the collection of transformation functions. The attribute names that are used, natively, to make the wrapper are _key_of_id, _id_of_key, _obj_of_data, _data_of_obj, _preset, and _postget.

If your trans_obj uses different names for these functions, you can use the add_aliases function. We’ll demo the use of add_aliases here:

>>> from dol import kv_wrap, add_aliases, Pipe
>>> from functools import partial
>>>
>>> class SeparatorTrans:
...     def __init__(self, sep: str):
...         self.sep = sep
...     def string_to_tuple(self, string: str):
...         return tuple(string.split(self.sep))
...     def tuple_to_string(self, tup: tuple):
...         return self.sep.join(tup)
>>>
>>> _add_aliases = partial(
...     add_aliases, _key_of_id='string_to_tuple', _id_of_key='tuple_to_string'
... )
>>> mk_sep_trans = Pipe(SeparatorTrans, _add_aliases, kv_wrap)
>>> sep_trans = mk_sep_trans('/')
>>> d = sep_trans({'a/b/c': 1, 'd/e': 2})
>>> list(d)
[('a', 'b', 'c'), ('d', 'e')]
>>> d['d', 'e']
2

kv_wrap also has convenience attributes (outcoming_keys, ingoing_keys, outcoming_vals, ingoing_vals, and val_reads_wrt_to_keys) which will only add a single specific wrapper (specified as a function), when that’s what you need.

dol.trans.kv_wrap_persister_cls(persister_cls, name=None)

Make a class that wraps a persister into a dol.base.Store,

Parameters:

persister_cls – The persister class to wrap

Returns:

A Store wrapping the persister (see dol.base)

>>> A = kv_wrap_persister_cls(dict)
>>> a = A()
>>> a['one'] = 1
>>> a['two'] = 2
>>> a['three'] = 3
>>> list(a.items())
[('one', 1), ('two', 2), ('three', 3)]
>>> assert hasattr(a, '_obj_of_data')  # for example, it has this magic method
>>> # If you overwrite the _obj_of_data method, you'll transform outcomming values with it.
>>> # For example, say the data you stored were minutes, but you want to get then in secs...
>>> a._obj_of_data = lambda data: data * 60
>>> list(a.items())
[('one', 60), ('two', 120), ('three', 180)]
>>>
>>> # And if you want to have class that has this weird "store minutes, retrieve seconds", you can do this:
>>> class B(kv_wrap_persister_cls(dict)):
...     def _obj_of_data(self, data):
...         return data * 60
>>> b = B()
>>> b.update({'one': 1, 'two': 2, 'three': 3})  # you can write several key-value pairs at once this way!
>>> list(b.items())
[('one', 60), ('two', 120), ('three', 180)]
>>> # Warning! Advanced under-the-hood chat coming up.... Note this:
>>> print(b)
{'one': 1, 'two': 2, 'three': 3}
>>> # What?!? Well, remember, printing an object calls the objects __str__, which usually calls __repr__
>>> # The wrapper doesn't wrap those methods, since they don't have consistent behaviors.
>>> # Here you're getting the __repr__ of the underlying dict store, without the key and value transforms.
>>>
>>> # Say you wanted to transform the incoming minute-unit data, converting to secs BEFORE they were stored...
>>> class C(kv_wrap_persister_cls(dict)):
...     def _data_of_obj(self, obj):
...         return obj * 60
>>> c = C()
>>> c.update(one=1, two=2, three=3)  # yet another way you can write multiple key-vals at once
>>> list(c.items())
[('one', 60), ('two', 120), ('three', 180)]
>>> print(c)  # but notice that unlike when we printed b, here the stored data is actually transformed!
{'one': 60, 'two': 120, 'three': 180}
>>>
>>> # Now, just to demonstrate key transformation, let's say that we need internal (stored) keys to be upper case,
>>> # but external (the keys you see when listed) ones to be lower case, for some reason...
>>> class D(kv_wrap_persister_cls(dict)):
...     _data_of_obj = staticmethod(lambda obj: obj * 60)  # to demonstrated another way of doing this
...     _key_of_id = lambda self, _id: _id.lower()  # note if you don't specify staticmethod, 1st arg must be self
...     def _id_of_key(self, k):  # a function definition like you're used to
...         return k.upper()
>>> d = D()
>>> d['oNe'] = 1
>>> d.update(TwO=2, tHrEE=3)
>>> list(d.items())  # you see clean lower cased keys at the interface of the store
[('one', 60), ('two', 120), ('three', 180)]
>>> # but internally, the keys are all upper case
>>> print(d)  # equivalent to print(d.store), so keys and values not wrapped (values were transformed before stored)
{'ONE': 60, 'TWO': 120, 'THREE': 180}
>>>
>>> # On the other hand, careful, if you gave the data directly to D, you wouldn't get that.
>>> d = D({'one': 1, 'two': 2, 'three': 3})
>>> print(d)
{'one': 1, 'two': 2, 'three': 3}
>>> # Thus is because when you construct a D with the dict, it initializes the dicts data with it directly
>>> # before the key/val transformers are in place to do their jobs.

dol.trans.leveled_paths_walk(m, levels)

Yield the key paths of m, down to levels levels.

dol.trans.mk_confirm_overwrite_preset(*, get_input=None, prompt=<function _dflt_overwrite_prompt>)

Make a wrap_kvs preset that asks for confirmation before overwriting an existing key that holds a different value.

The returned preset writes v unchanged unless k already maps to a different value; in that case it asks get_input to confirm (by typing the new value), and keeps the existing value if the confirmation doesn’t match. Use get_input to customize how confirmation is obtained (None -> the builtin input, resolved at call time), e.g. for testing or for a non-interactive policy. See confirm_overwrite().

>>> store = dict(a='apple', b='banana')
>>> # simulate a user who always types the exact new value (confirms every overwrite)
>>> always_yes = wrap_kvs(
...     store, preset=mk_confirm_overwrite_preset(get_input=lambda prompt: 'alligator')
... )
>>> always_yes['a'] = 'alligator'   # confirmation matches -> overwrites
>>> store['a']
'alligator'
>>> # simulate a user who declines (types something that doesn't match)
>>> always_no = wrap_kvs(
...     store, preset=mk_confirm_overwrite_preset(get_input=lambda prompt: 'nope')
... )
>>> always_no['a'] = 'anteater'     # declined -> existing value kept
>>> store['a']
'alligator'

dol.trans.mk_kv_reader_from_kv_collection(kv_collection, name=None, getitem=<function transparent_key_method>)

Make a KvReader class from a Collection class.

Parameters:

• kv_collection – The Collection class

• name – The name to give the KvReader class (by default, it will be kv_collection.__qualname__ + ‘Reader’)

• getitem – The method that will be assigned to __getitem__. Should have the (self, k) signature. By default, getitem will be transparent_key_method, returning the key as is. This default is useful when you want to delegate the actual getting to a _obj_of_data wrapper.

Returns:

A KvReader class that subclasses the input kv_collection

dol.trans.mk_level_walk_filt(levels)

Makes a walk_filt function for kv_walk based on some level logic. If levels is an integer, will consider it as the max path length, if not it will just assert that levels is callable, and return it

dol.trans.mk_read_only(o)

Disable __setitem__ and __delitem__ on o (a store class, typically).

>>> class D(dict):
...     pass
>>> D = mk_read_only(D)
>>> D()['a'] = 1
Traceback (most recent call last):
  ...
ValueError: writing is disabled

dol.trans.mk_trans_obj(**kwargs)

Convenience method to quickly make a trans_obj (just an object holding some trans functions

dol.trans.mk_wrapper(wrap_cls)

You have a wrapper class and you want to make a wrapper out of it, that is, a decorator factory with which you can make wrappers, like this:

wrapper = mk_wrapper(wrap_cls)

that you can then use to transform stores like thiis:

MyStore = wrapper(**wrapper_kwargs)(StoreYouWantToTransform)

Parameters:

wrap_cls

Returns:

>>> class RelPath:
...     def __init__(self, root):
...         self.root = root
...         self._root_length = len(root)
...     def _key_of_id(self, _id):
...         return _id[self._root_length:]
...     def _id_of_key(self, k):
...         return self.root + k
>>> relpath_wrap = mk_wrapper(RelPath)
>>> RelDict = relpath_wrap(root='foo/')(dict)
>>> s = RelDict()
>>> s['bar'] = 42
>>> assert list(s) == ['bar']
>>> assert s['bar'] == 42
>>> assert str(s) == "{'foo/bar': 42}"  # reveals that actually, behind the scenes, there's a "foo/" prefix

dol.trans.raise_disabled_error(functionality)

Make a function that raises ValueError('<functionality> is disabled') whenever called.

dol.trans.redirect_getattr_to_getitem(cls=None, *, keys_have_priority_over_attributes=False, __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

A mapping decorator that redirects attribute access to __getitem__.

Warning

This decorator will make your class un-pickleable.

Parameters:

keys_have_priority_over_attributes – If True, keys will have priority over existing attributes.

>>> @redirect_getattr_to_getitem
... class MyDict(dict):
...     pass
>>> d = MyDict(a=1, b=2)
>>> d.a
1
>>> d.b
2
>>> list(d)
['a', 'b']

dol.trans.return_default_if_error(store=None, *, default=None, errors=(<class 'KeyError'>, ))

Wrap store so that __getitem__ errors in errors return default instead of raising.

dol.trans.store_decorator(func)

Helper to make store decorators.

You provide a class-decorating function func that takes a store type (and possibly additional params) and returns another decorated store type.

store_decorator takes that func and provides an enhanced class decorator specialized for stores. Namely it will:

• Add __module__, __qualname__, __name__ and __doc__ arguments to it

• Copy the aforementioned arguments to the decorated class, or copy the attributes of the original if not specified.

• Output a decorator that can be used in four different ways: a class/instance decorator/factory.

By class/instance decorator/factory we mean that if A is a class, a an instance of it, and deco a decorator obtained with store_decorator(func), we can use deco to

• class decorator: decorate a class

• class decorator factory: make a function that decorates classes

• instance decorator: decorate an instance of a store

• instancce decorator factor: make a function that decorates instances of stores

For example, say we have the following deco that we made with store_decorator:

>>> @store_decorator
... def deco(cls=None, *, x=1):
...     # do stuff to cls, or a copy of it...
...     cls.x = x  # like this for example
...     return cls

And a class that has nothing to it:

>>> class A: ...

Nammely, it doesn’t have an x

>>> hasattr(A, 'x')
False

We make a decorated_A with deco (class decorator example)

>>> t = deco(A, x=42)
>>> assert isinstance(t, type)

and we see that we now have an x and it’s 42

>>> hasattr(A, 'x')
True
>>> A.x
42

But we could have also made a factory to decorate A and anything else that comes our way.

>>> paint_it_42 = deco(x=42)
>>> decorated_A = paint_it_42(A)
>>> assert decorated_A.x == 42
>>> class B:
...     x = 'destined to disappear'
>>> assert paint_it_42(B).x == 42

To be fair though, you’ll probably see the factory usage appear in the following form, where the class is decorated at definition time.

>>> @deco(x=42)
... class B:
...     pass
>>> assert B.x == 42

If your exists already, and you want to keep it as is (with the same name), you can use subclassing to transform a copy of A instead, as below. Also note in the following example, that deco was used without parentheses, which is equivalent to @deco(), and yes, store_decorator makes that possible to, as long as your params have defaults

>>> @deco
... class decorated_A(A):
...     pass
>>> assert decorated_A.x == 1
>>> assert A.x == 42

Finally, you can also decorate instances:

>>> class A: ...
>>> a = A()
>>> hasattr(a, 'x')
False
>>> b = deco(a); assert b.x == 1; # b has an x and it's 1
>>> b = deco()(a); assert b.x == 1; # b has an x and it's 1
>>> b = deco(a, x=42); assert b.x == 42  # b has an x and it's 42
>>> b = deco(x=42)(a); assert b.x == 42; # b has an x and it's 42

Warning

Note though that the type of b is not the same type as a

>>> isinstance(b, a.__class__)
False

No, b is an instance of a dol.base.Store, which is a class containing an instance of a store (here, a).

>>> type(b)
<class 'dol.base.Store'>
>>> b.store == a
True

Now, here’s some more example, slightly closer to real usage

>>> from dol.trans import store_decorator
>>> from inspect import signature
>>>
>>> def rm_deletion(store=None, *, msg='Deletions not allowed.'):
...     name = getattr(store, '__name__', 'Something') + '_w_sommething'
...     assert isinstance(store, type), f"Should be a type, was {type(store)}: {store}"
...     wrapped_store = type(name, (store,), {})
...     wrapped_store.__delitem__ = lambda self, k: msg
...     return wrapped_store
...
>>> remove_deletion = store_decorator(rm_deletion)

See how the signature of the wrapper has some extra inputs that were injected (__module__, __qualname__, etc.):

>>> print(str(signature(remove_deletion)))
(store=None, *, msg='Deletions not allowed.', __module__=None, __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Using it as a class decorator factory (the most common way):

As a class decorator “factory”, without parameters (and without ()):

>>> from collections import UserDict
>>> @remove_deletion
... class WD(UserDict):
...     "Here's the doc"
...     pass
>>> wd = WD(x=5, y=7)
>>> assert wd == UserDict(x=5, y=7)  # same as far as dict comparison goes
>>> assert wd.__delitem__('x') == 'Deletions not allowed.'
>>> assert wd.__doc__ == "Here's the doc"

As a class decorator “factory”, with parameters:

>>> @remove_deletion(msg='No way. I do not trust you!!')
... class WD(UserDict): ...
>>> wd = WD(x=5, y=7)
>>> assert wd == UserDict(x=5, y=7)  # same as far as dict comparison goes
>>> assert wd.__delitem__('x') == 'No way. I do not trust you!!'

The __doc__ is empty:

>>> assert WD.__doc__ == None

But we could specify a doc if we wanted to:

>>> @remove_deletion(__doc__="Hi, I'm a doc.")
... class WD(UserDict):
...     "This is the original doc, that will be overritten"
>>> assert WD.__doc__ == "Hi, I'm a doc."

The class decorations above are equivalent to the two following:

>>> WD = remove_deletion(UserDict)
>>> wd = WD(x=5, y=7)
>>> assert wd == UserDict(x=5, y=7)  # same as far as dict comparison goes
>>> assert wd.__delitem__('x') == 'Deletions not allowed.'
>>>
>>> WD = remove_deletion(UserDict, msg='No way. I do not trust you!!')
>>> wd = WD(x=5, y=7)
>>> assert wd == UserDict(x=5, y=7)  # same as far as dict comparison goes
>>> assert wd.__delitem__('x') == 'No way. I do not trust you!!'

But we can also decorate instances. In this case they will be wrapped in a Store class before being passed on to the actual decorator.

>>> d = UserDict(x=5, y=7)
>>> wd = remove_deletion(d)
>>> assert wd == d  # same as far as dict comparison goes
>>> assert wd.__delitem__('x') == 'Deletions not allowed.'
>>>
>>> d = UserDict(x=5, y=7)
>>> wd = remove_deletion(d, msg='No way. I do not trust you!!')
>>> assert wd == d  # same as far as dict comparison goes
>>> assert wd.__delitem__('x') == 'No way. I do not trust you!!'

dol.trans.store_wrap(obj)

Wrap a class or an instance in a Store (a class gets a Store subclass whose __init__ builds the wrapped instance).

dol.trans.take_everything(key)

Key filter that accepts every key.

dol.trans.transparent_key_method(self, k)

Return the key as is (the default getitem of mk_kv_reader_from_kv_collection).

dol.trans.warn_and_ignore_if_error(store=None, *, errors=(<class 'KeyError'>, ), warn_msg='Ignoring error in __getitem__ for key {k}: {e}')

Like ignore_if_error, but also emit a warning (warn_msg) for each ignored error.

dol.trans.wrap_kvs(store=None, *, wrapper=None, name=None, key_of_id=None, id_of_key=None, obj_of_data=None, data_of_obj=None, preset=None, postget=None, key_codec=None, value_codec=None, key_encoder=None, key_decoder=None, value_encoder=None, value_decoder=None, __module__=None, outcoming_key_methods=(), outcoming_value_methods=(), ingoing_key_methods=(), ingoing_value_methods=(), __name__=None, __qualname__=None, __doc__=None, __annotations__=None, __defaults__=None, __kwdefaults__=None)

Make a Store that is wrapped with the given key/val transformers.

Naming convention:

Morphemes:
    key: outer key
    _id: inner key
    obj: outer value
    data: inner value
Grammar:
    Y_of_X: means that you get a Y output when giving an X input. Also known as X_to_Y.

Parameters:

• store – Store class or instance

• name – Name to give the wrapper class

• key_of_id – The outcoming key transformation function. Forms are k = key_of_id(_id) or k = key_of_id(self, _id)

• id_of_key – The ingoing key transformation function. Forms are _id = id_of_key(k) or _id = id_of_key(self, k)

• obj_of_data – The outcoming val transformation function. Forms are obj = obj_of_data(data) or obj = obj_of_data(self, data)

• data_of_obj – The ingoing val transformation function. Forms are data = data_of_obj(obj) or data = data_of_obj(self, obj)

• preset –

  A function that is called before doing a __setitem__. The function is called with both k and v as inputs, and should output a transformed value. The intent use is to do ingoing value transformations conditioned on the key. For example, you may want to serialize an object depending on if you’re writing to a ‘.csv’, or ‘.json’, or ‘.pickle’ file.

  Forms are preset(k, obj) or preset(self, k, obj)

• postget – A function that is called after the value v for a key k is be __getitem__. The function is called with both k and v as inputs, and should output a transformed value. The intent use is to do outcoming value transformations conditioned on the key. We already have obj_of_data for outcoming value trans, but cannot condition it’s behavior on k. For example, you may want to deserialize the bytes of a ‘.csv’, or ‘.json’, or ‘.pickle’ in different ways. Forms are obj = postget(k, data) or obj = postget(self, k, data)

Returns:

A key and/or value transformed wrapped (or wrapper) class (or instance).

>>> def key_of_id(_id):
...     return _id.upper()
>>> def id_of_key(k):
...     return k.lower()
>>> def obj_of_data(data):
...     return data - 100
>>> def data_of_obj(obj):
...     return obj + 100
>>>
>>> A = wrap_kvs(dict, name='A',
...             key_of_id=key_of_id, id_of_key=id_of_key, obj_of_data=obj_of_data, data_of_obj=data_of_obj)
>>> a = A()
>>> a['KEY'] = 1
>>> a  # repr is just the base class (dict) repr, so shows "inside" the store (lower case keys and +100)
{'key': 101}
>>> a['key'] = 2
>>> print(a)  # repr is just the base class (dict) repr, so shows "inside" the store (lower case keys and +100)
{'key': 102}
>>> a['kEy'] = 3
>>> a  # repr is just the base class (dict) repr, so shows "inside" the store (lower case keys and +100)
{'key': 103}
>>> list(a)  # but from the point of view of the interface the keys are all upper case
['KEY']
>>> list(a.items())  # and the values are those we put there.
[('KEY', 3)]
>>>
>>> # And now this: Showing how to condition the value transform (like obj_of_data), but conditioned on key.
>>> B = wrap_kvs(dict, name='B', postget=lambda k, v: f'upper {v}' if k[0].isupper() else f'lower {v}')
>>> b = B()
>>> b['BIG'] = 'letters'
>>> b['small'] = 'text'
>>> list(b.items())
[('BIG', 'upper letters'), ('small', 'lower text')]
>>>
>>>
>>> # Let's try preset and postget. We'll wrap a dict and write the same list of lists object to
>>> # keys ending with .csv, .json, and .pkl, specifying the obvious extension-dependent
>>> # serialization/deserialization we want to associate with it.
>>>
>>> # First, some very simple csv transformation functions
>>> to_csv = lambda LoL: '\\n'.join(map(','.join, map(lambda L: (x for x in L), LoL)))
>>> from_csv = lambda csv: list(map(lambda x: x.split(','), csv.split('\\n')))
>>> LoL = [['a','b','c'],['d','e','f']]
>>> assert from_csv(to_csv(LoL)) == LoL
>>>
>>> import json, pickle
>>>
>>> def preset(k, v):
...     if k.endswith('.csv'):
...         return to_csv(v)
...     elif k.endswith('.json'):
...         return json.dumps(v)
...     elif k.endswith('.pkl'):
...         return pickle.dumps(v)
...     else:
...         return v  # as is
...
...
>>> def postget(k, v):
...     if k.endswith('.csv'):
...         return from_csv(v)
...     elif k.endswith('.json'):
...         return json.loads(v)
...     elif k.endswith('.pkl'):
...         return pickle.loads(v)
...     else:
...         return v  # as is
...
>>> mydict = wrap_kvs(dict, preset=preset, postget=postget)
>>>
>>> obj = [['a','b','c'],['d','e','f']]
>>> d = mydict()
>>> d['foo.csv'] = obj  # store the object as csv
>>> d  # "printing" a dict by-passes the transformations, so we see the data in the "raw" format it is stored in.
{'foo.csv': 'a,b,c\\nd,e,f'}
>>> d['foo.csv']  # but if we actually ask for the data, it deserializes to our original object
[['a', 'b', 'c'], ['d', 'e', 'f']]
>>> d['bar.json'] = obj  # store the object as json
>>> d
{'foo.csv': 'a,b,c\\nd,e,f', 'bar.json': '[["a", "b", "c"], ["d", "e", "f"]]'}
>>> d['bar.json']
[['a', 'b', 'c'], ['d', 'e', 'f']]
>>> d['bar.json'] = {'a': 1, 'b': [1, 2], 'c': 'normal json'}  # let's write a normal json instead.
>>> d
{'foo.csv': 'a,b,c\\nd,e,f', 'bar.json': '{"a": 1, "b": [1, 2], "c": "normal json"}'}
>>> del d['foo.csv']
>>> del d['bar.json']
>>> d['foo.pkl'] = obj  # 'save' obj as pickle
>>> d['foo.pkl']
[['a', 'b', 'c'], ['d', 'e', 'f']]