[ python-Bugs-1283289 ] PyArg_ParseTupleAndKeywords gives misleading error message

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Bugs item #1283289, was opened at 2005-09-06 21:12
Message generated for change (Comment added) made by loewis
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Category: Extension Modules
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: japierro (japierro)
Assigned to: Martin v. Löwis (loewis)
Summary: PyArg_ParseTupleAndKeywords gives misleading error message

Initial Comment:
Python 2.3.3 on Windows XP

If the user supplies one valid and one invalid keyword to 
a function that defines two required keyword arguments, 
PyArg_ParseTupleAndKeywords will raise this 
exception:

TypeError: function takes exactly 2 arguments (1 given)

If, in getargs.c, vgetargskeywords, the check 
for "extraneous keywords" were done near the top of the 
function, a more meaningful exception would be thrown:

TypeError: 'bad' is an invalid keyword argument for this 
function


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>Comment By: Martin v. Löwis (loewis)
Date: 2005-12-27 14:48

Message:
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I agree that the error message should be fixed; this is even
an 'XXX' comment ("an this isn't a bug?").

Unfortunately, just looking for bad keyword arguments is not
enough - it might even be that an optional keyword argument
is supplied, and still the error message is confusing, e.g. for

>>> re.compile("a").match(pos=10)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: match() takes at least 1 argument (0 given)

Instead, I think the error message should read: 

TypeError: "pattern" argument for match() is missing

as we know exactly what "meaning" the missing argument has.

This might still be unspecific if multiple required
arguments are missing, but I think just giving the first one
would be informative enough - or else it could read

TypeError: "pattern" argument for match() is missing (+2 more)

if there are 2 more missing.

Yet alternatively, it could read

TypeError: required arguments for match() missing:
'pattern', 'foo', 'bar'

Patches in this direction are welcome; the precise wording
proposal should be mentioned on python-dev.

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Comment By: Reinhold Birkenfeld (birkenfeld)
Date: 2005-12-16 20:43

Message:
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Any opinions?

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