Marco Buttu added the comment:
The documentation [1] says: "If a variable is used in a code block but not
defined there, it is a free variable." According to this description, it seems
to me that the variable ``x`` is free in ``foo()``::
>>> def foo():
... print(x)
But actually for the code object it is not::
>>> foo.__code__.co_freevars
()
The meaning of free variable used for the code object is consistent with the
``locals()`` documentation [2]: "Free variables are returned by locals() when
it is called in function blocks". In fact, in the following code ``x` is not a
free variable for ``locals()``::
>>> def foo():
... print(x)
... print(locals())
...
>>> x = 3
>>> foo()
3
{}
So, I thing there is an inconsistency between the definition of "free variable"
given in [1] and the meaning of "free variable" both in the code object and in
the ``locals()`` documentation [2].
But if we change the definition of "free variable" according to the meaning of
both the code object and ``locals()``, I am afraid we go in the wrong
direction, because I suspect for most people the proper definition of free
variable is the one given in [1]. Also for Wikipedia [3]: "In computer
programming, the term free variable refers to variables used in a function that
are neither local variables nor parameters of that function.".
Instead, if we keep or remove the definition of "free variable" given in [1], I
agree with Terry to change the ``locals()`` documentation, writing that
"``locals()`` includes also the locals of the surrounding function contexts,
even though they are called 'nonlocal' within the nested function.". Maybe it
is also worth adding a shell example, to better clarify.
So, at the end, to me the ideal solution would be to keep in [1] the current
definition of "free variable", to change the ``locals()`` documentation
according to Terry suggestion, and to change the behavior of
``code.co_freevars`` (maybe not only this) in order to fit the definition.
[1] https://docs.python.org/3/reference/executionmodel.html#naming-and-binding
[2] https://docs.python.org/3/library/functions.html#locals
[3] https://en.wikipedia.org/wiki/Free_variables_and_bound_variables
----------
nosy: +marco.buttu
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<http://bugs.python.org/issue26683>
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