dol.dig

Layers introspection

dol.dig.trace_getitem(store, k, layer_attrs=('store'))

A generator of layered steps to inspect a store.

Parameters

• store – An instance that has the base.Store interface

• k – A key

• layer_attrs – The attribute names that should be checked to get the next layer.

Returns

A generator of (layer, method, value)

We start with a small dict:

>>> d = {'a.num': '1000', 'b.num': '2000'}

Now let’s add layers to it. For example, with wrap_kvs:

>>> from dol.trans import wrap_kvs

Say that we want the interface to not see the '.num' strings, and deal with numerical values, not strings.

>>> s = wrap_kvs(d,
...              key_of_id=lambda x: x[:-len('.num')],
...              id_of_key=lambda x: x + '.num',
...              obj_of_data=lambda x: int(x),
...              data_of_obj=lambda x: str(x)
...             )
>>>

Oh, and we want the interface to display upper case keys.

>>> ss = wrap_kvs(s,
...              key_of_id=lambda x: x.upper(),
...              id_of_key=lambda x: x.lower(),
...             )

And we want the numerical unit to be the kilo (that’s 1000):

>>> sss = wrap_kvs(ss,
...                obj_of_data=lambda x: x / 1000,
...                data_of_obj=lambda x: x * 1000
...               )
>>>
>>> dict(sss.items())
{'A': 1.0, 'B': 2.0}

Well, if we had bugs, we’d like to inspect the various layers, and how they transform the data.

# Here's how to do that:

# >>> for layer, method, value in trace_getitem(sss, 'A'):
# ...     print(layer, method, value)
# ...
# Traceback (most recent call last):
#   File "<stdin>", line 1, in <module>
# NameError: name 'trace_getitem' is not defined

>>> from dol.dig import trace_getitem
>>>
>>> for layer, method, value in trace_getitem(sss, 'A'):
...     print(layer, method, value)
...
{'a.num': '1000', 'b.num': '2000'} _id_of_key A
{'a.num': '1000', 'b.num': '2000'} _id_of_key A
{'a.num': '1000', 'b.num': '2000'} _id_of_key a
{'a.num': '1000', 'b.num': '2000'} _id_of_key a
{'a.num': '1000', 'b.num': '2000'} _id_of_key a.num
{'a.num': '1000', 'b.num': '2000'} _id_of_key a.num
{'a.num': '1000', 'b.num': '2000'} __getitem__ 1000
{'a.num': '1000', 'b.num': '2000'} _obj_of_data 1000
{'a.num': '1000', 'b.num': '2000'} _obj_of_data 1000
{'a.num': '1000', 'b.num': '2000'} _obj_of_data 1000
{'a.num': '1000', 'b.num': '2000'} _obj_of_data 1000
{'a.num': '1000', 'b.num': '2000'} _obj_of_data 1000
{'a.num': '1000', 'b.num': '2000'} _obj_of_data 1.0