8000 [3.9] Add more tests to the descriptor howto guide (GH-23506) by miss-islington · Pull Request #23510 · python/cpython · GitHub
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8000 [3.9] Add more tests to the descriptor howto guide (GH-23506) #23510

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Nov 25, 2020
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[3.9] Add more tests to the descriptor howto guide (GH-23506) #23510

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29 changes: 25 additions & 4 deletions Doc/howto/descriptor.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -170,7 +170,15 @@ the lookup or update:


An interactive session shows that all access to the managed attribute *age* is
logged, but that the regular attribute *name* is not logged::
logged, but that the regular attribute *name* is not logged:

.. testcode::
:hide:

import logging, sys
logging.basicConfig(level=logging.INFO, stream=sys.stdout, force=True)

.. doctest::

>>> mary = Person('Mary M', 30) # The initial age update is logged
INFO:root:Updating 'age' to 30
Expand Down Expand Up @@ -256,7 +264,15 @@ we call :func:`vars` to look up the descriptor without triggering it:
>>> vars(vars(Person)['age'])
{'public_name': 'age', 'private_name': '_age'}

The new class now logs access to both *name* and *age*::
The new class now logs access to both *name* and *age*:

.. testcode::
:hide:

import logging, sys
logging.basicConfig(level=logging.INFO, stream=sys.stdout, force=True)

.. doctest::

>>> pete = Person('Peter P', 10)
INFO:root:Updating 'name' to 'Peter P'
Expand Down Expand Up @@ -433,7 +449,9 @@ Here's how the data validators can be used in a real class:
self.kind = kind
self.quantity = quantity

The descriptors prevent invalid instances from being created::
The descriptors prevent invalid instances from being created:

.. doctest::

>>> Component('Widget', 'metal', 5) # Blocked: 'Widget' is not all uppercase
Traceback (most recent call last):
Expand Down Expand Up @@ -1227,7 +1245,10 @@ Now a new dictionary of unique keys can be constructed like this:

.. doctest::

>>> Dict.fromkeys('abracadabra')
>>> d = Dict.fromkeys('abracadabra')
>>> type(d) is Dict
True
>>> d
{'a': None, 'b': None, 'r': None, 'c': None, 'd': None}

Using the non-data descriptor protocol, a pure Python version of
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