dol.mixins

Mixins

class dol.mixins.FilteredKeysMixin

Filters __iter__ and __contains__ with (the boolean filter function attribute) _key_filt.

class dol.mixins.IdentityKeysWrapMixin

Transparent KeysWrapABC. Often placed in the mro to satisfy the KeysWrapABC need in a neutral way. This is useful in cases where the keys the persistence functions work with are the same as those you want to work with.

class dol.mixins.IdentityKvWrapMixin

Transparent Keys and Vals Wrap

class dol.mixins.IdentityValsWrapMixin

Transparent ValsWrapABC. Often placed in the mro to satisfy the KeysWrapABC need in a neutral way. This is useful in cases where the values can be persisted by __setitem__ as is (or the serialization is handled somewhere in the __setitem__ method.

class dol.mixins.IterBasedSizedContainerMixin

An ABC that defines

1. how to iterate over a collection of elements (keys) (__iter__)

2. check that a key is contained in the collection (__contains__), and

3. how to get the number of elements in the collection

This is exactly what the collections.abc.Collection (from which Keys inherits) does. The difference here, besides the “Keys” purpose-explicit name, is that Keys offers default

__len__ and __contains__ definitions based on what ever __iter__ the concrete class defines.

Keys is a collection (i.e. a Sized (has __len__), Iterable (has __iter__), Container (has __contains__). It’s purpose is to serve as a collection of object identifiers in a key->obj mapping. The Keys class doesn’t implement __iter__ (so needs to be subclassed with a concrete class), but offers mixin __len__ and __contains__ methods based on a given __iter__ method. Note that usually __len__ and __contains__ should be overridden to more, context-dependent, efficient methods.

class dol.mixins.OverWritesNotAllowedMixin

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.mixins.ReadOnlyMixin

Put this as your first parent class to disallow write/delete operations

class dol.mixins.SimpleJsonMixin

simple json serialization. Useful to store and retrieve

class dol.mixins.StringKvWrap