[Python-Dev] The interpreter accepts f(**{'5':'foo'}); is this intentional?

[Calvin Spealman]

I would favor this not being constrained. I don't want every use of **
to cause a pattern match to verify each key. I would even be fine
without the check for being strings. Define what it should be, but let
the implementation be lax. It is no different from any other place
where you need to know its not a promise, just an artifact, and
shouldn't rely on what the implementation currently does or does not
force.

On Thu, Feb 5, 2009 at 3:03 AM, Michael Haggerty <mhagger at alum.mit.edu> wrote:
> I can't find documentation about whether there are constraints imposed
> on the keys in the map passed to a function via **, as in f(**d).
>
> According to
>
>    http://docs.python.org/reference/expressions.html#id9
>
> , d must be a mapping.
>
> test_extcall.py implies that the keys of this map must be strings in the
> following test:
>
>    >>> f(**{1:2})
>    Traceback (most recent call last):
>      ...
>    TypeError: f() keywords must be strings
>
> But must the keys be valid python identifiers?
>
> In particular, the following is allows by the Python 2.5.2 and the
> Jython 2.2.1 interpreters:
>
>    >>> f(**{'1':2})
>    {'1': 2}
>
> Is this behavior required somewhere by the Python language spec, or is
> it an error that just doesn't happen to be checked, or is it
> intentionally undefined whether this is allowed?
>
> Michael
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