[New-bugs-announce] [issue8419] dict constructor allows invalid identifiers in **kwargs

[Mark Dickinson]

New submission from Mark Dickinson <dickinsm at gmail.com>:

In all versions of CPython right now, the following works.

>>> dict({1:2}, **{3:4})
{1: 2, 3: 4}

Other Python implementations raise TypeError for this;  CPython should probably do the same, beginning with deprecating this behaviour in Python 3.2 and removing it in 3.3.

>From a python-dev posting[1] by Alex Gaynor:

"""
I ran into the follow behavior while making sure Django works
correctly on PyPy.  The following behavior was observed in all tested
versions of CPython (2.5, 3.1):

>>> def f(**kwargs):
...     print(kwargs)
...
>>> kwargs = {1: 3}
>>>
>>> dict({}, **kwargs)
{1: 3}
>>> f(**kwargs)
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
TypeError: f() keywords must be strings
>>>

This behavior seems pretty strange to me, indeed PyPy gives the
TypeError for both attempts.  I just wanted to confirm that it was in
fact intentional.
"""

Raghuram Devarakonda says (in the same python-dev thread):

"I ran into same issue with Django on Jython yesterday [1] since Jython
too gives TypeError for 'dict({}, **kwargs)'."

Guido, on the suggestion that both the CPython and PyPy behaviour be left as is, and that the behaviour be regarded as implementation defined:

"That is just going to cause some programs to have a portability
surprise. I think one or the other should be fixed. I am fine with declaring dict({}, **{1:3}) illegal, since after all it is abuse of the ** mechanism. We should deprecate it in at least one version though."


[1] http://mail.python.org/pipermail/python-dev/2010-April/099427.html

----------
components: Interpreter Core
messages: 103330
nosy: mark.dickinson
priority: normal
severity: normal
stage: unit test needed
status: open
title: dict constructor allows invalid identifiers in **kwargs
type: behavior
versions: Python 3.2, Python 3.3

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue8419>
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