[Python-Dev] Very Strange Argument Handling Behavior (original) (raw)

Guido van Rossum guido at python.org
Sat Apr 17 17:27:18 CEST 2010

On Sat, Apr 17, 2010 at 5:41 AM, Vinay Sajip <vinay_sajip at yahoo.co.uk> wrote:

Steve Holden <steve holdenweb.com> writes:

I'm sure we wouldn't want to go so far as to inhibit this. (Py 3.1)

>>> def f(**kwargs): ...   kwargs[1] = "dummy" ...   print(kwargs) ... >>> f(this="Guido", that="Raymond", theother="Steve") {'this': 'Guido', 1: 'dummy', 'theother': 'Steve', 'that': 'Raymond'} I think that according to the proposal, the above snippet would be OK, but def f(**kwargs):  kwargs[1] = 'dummy'  g(**kwargs) would fail at the call of g.

And that is already the status quo. Try it out in your friendly Python interpreter.

The only thing that should be changed is for the dict() builtin to insist that if it receives a dict containing keyword arguments the keys must all be strings. This only affects the dict() builtin. It has keyword arguments so that instead of {'foo': 1, 'bar': 2} you can write dict(foo=1, bar=2), which arguably is more readable because it doesn't have so many quotes. OTOH calling dict(x, **y) is a weird hack. Note that if you wrote a wrapper function in Python around dict() with the same behavior there would be no way to prevent the check that all the keys are strings.

-- --Guido van Rossum (python.org/~guido)

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