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gh-120452: improve documentation about private name mangling (#120451)

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Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
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Bénédikt Tran 2024-07-13 16:45:18 +02:00 • committed by GitHub
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Doc/faq/programming.rst
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@ -1741,11 +1741,31 @@ but effective way to define class private variables. Any identifier of the form
is textually replaced with ``_classname__spam``, where ``classname`` is the
current class name with any leading underscores stripped.
This doesn't guarantee privacy: an outside user can still deliberately access
the "_classname__spam" attribute, and private values are visible in the object's
``__dict__``. Many Python programmers never bother to use private variable
names at all.
The identifier can be used unchanged within the class, but to access it outside
the class, the mangled name must be used:
.. code-block:: python
class A:
def __one(self):
return 1
def two(self):
return 2 * self.__one()
class B(A):
def three(self):
return 3 * self._A__one()
four = 4 * A()._A__one()
In particular, this does not guarantee privacy since an outside user can still
deliberately access the private attribute; many Python programmers never bother
to use private variable names at all.
.. seealso::
The :ref:`private name mangling specifications <private-name-mangling>`
for details and special cases.
My class defines __del__ but it is not called when I delete the object.
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