[Python-porting] co_names behavior change

[Brett Cannon]

I'm not aware of a specific change, but the What's New documentation tries
to capture critical changes like this that would break someone's code.

On Mon, Apr 8, 2019 at 10:31 AM Tom Ekberg <tekberg at uw.edu> wrote:

> I'm using the roundup program which has been ported from Python 2.7 to
> Python 3.x. My group uses this program internally to track progress and
> document issues. Roundup is written in Python and has a templating language
> (TAL) that allows one to define a Python expression. This is implemented by
> constructing a function:
>
>
>             d = {}
>             exec('def f():\n return %s\n' % expr.strip(), d)
>             self._f = d['f']
>
> where expr contains the Python expression. To reference variables defined
> in the templating language it constructs a list of variable names using the
> names in self.__code__.co_names:
>
>
>         self._f_varnames = vnames = []
>         for vname in self._f.__code__.co_names:
>             if vname[0] not in '$_':
>
> This works fine for Python 2.7. However for Python 3.5, the value of
> self._f.__code__.co_names does not always contain all names referenced in
> the expression. When the function is executed it generates an exception
> saying that a variable being referenced is undefined. Some expression work
> correctly, some do not. I have documented an example that fails in the
> roundup bug tracking database:
> https://issues.roundup-tracker.org/issue2551026. I came up with a roundup
> patch that implements variation that works for both Python 2.7 and Python
> 3.5.
>
>
> My question to this group:
>
>
> Do you have knowledge of the different contents of __code__.co_names
> between Python 2.7 and Python 3.5? I'm expecting that this is a difference
> that is documented somewhere.
>
>
> I have attached an example that illustrates this problem.
>
>
> Tom Ekberg
> Senior Computer Specialist, Lab Medicine
> 4th Floor, Pat Steel Building
> Department of Laboratory Medicine
> Work: (206) 520-4856
> Email: tekberg at uw.edu
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