[ python-Patches-1686487 ] Allow any mapping after ** in calls

Patches item #1686487, was opened at 2007-03-23 03:27
Message generated for change (Comment added) made by gbrandl
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Category: Core (C code)
Group: Python 2.6
>Status: Closed
>Resolution: Accepted
Priority: 5
Private: No
Submitted By: Alexander Belopolsky (belopolsky)
Assigned to: Nobody/Anonymous (nobody)
Summary: Allow any mapping after ** in calls

Initial Comment:
Python allows arbitrary sequences after * in calls, but an expression following ** must be a (subclass of) dict.  The attached patch makes Python accept arbitrary mappings after **. 

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>Comment By: Georg Brandl (gbrandl)
Date: 2007-05-21 20:34

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I think it just needs someone to commit it. ;) See revision 55495.

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Comment By: Alexander Belopolsky (belopolsky)
Date: 2007-05-20 15:30

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What else needs to be done for the patch to go in?  Guido OKed the feature
and zseil gave a favorable code review.  Is there any reason not to apply
it?

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Comment By: Alexander Belopolsky (belopolsky)
Date: 2007-04-24 13:19

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zseil: It would be nice if it contained the information about kwdict's
type.

I agree, the new patch adds type information to both * and ** error
messages.
File Added: star-star-mapping-msg.patch

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Comment By: Ziga Seilnacht (zseil)
Date: 2007-04-24 10:32

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The patch looks good to me.  The only thing that could
be improved is the error message.  It would be nice if
it contained the information about kwdict's type.


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Comment By: Alexander Belopolsky (belopolsky)
Date: 2007-04-18 19:53

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File Added: star-star-mapping.patch

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Comment By: Alexander Belopolsky (belopolsky)
Date: 2007-04-18 19:38

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The proposed patch handles ** arguments similar to the way * arguments are
treated.  If the expression following ** evaluates to an object that is not
a dictionary, the new code attempts to update a new dictionary with that
object. This procedure is closely similar to what PySequence_Tuple does
with * arguments. (Python API does not provide PyMapping_Dict.) If new
dictionary is succesfully created and updated, it replaces the original **
argument. If that attempt fails because kwdict is not a mapping (does not
have a 'keys' attribute, a type error is raised explaining that a mapping
is expected.  All other errors, e.g. MemoryError are percolated up.

(I am am removing the previous versions of the patch.)
File Added: star-star-mapping.patch

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Comment By: Alexander Belopolsky (belopolsky)
Date: 2007-04-18 18:34

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Georg,

Thanks for reposting my proposal. Since BDFL is +1 on the idea, I feel
motivated to polish the patch.  In your early comment you noted that kwdict
== NULL check may be superficial.  I agree.  It does not look like it is
possible that ext_do_call is called with CALL_FLAG_KW set and a null
pointer at the top of the stack.  It looks like this may only happen if the
stack is corrupted by a misbehaving c extension.  In this case, however,
throwing a type error is too gentle. PyErr_BadInternalCall() seems to be
more appropriate if anything at all.

I propose to eliminate the null check for kwdict alltogether. This would
be consistent with the way stararg is handled later in this function.  I am
going to run the testsuit without the null check and will post a revised
patch shortly.




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Comment By: Alexander Belopolsky (belopolsky)
Date: 2007-04-18 16:02

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I have asked on python-dev almost a month ago, but did not get any
response:

http://mail.python.org/pipermail/python-dev/2007-March/072321.html

I have recently posted another message that got no response as well:

http://mail.python.org/pipermail/python-dev/2007-April/072653.html

Is it possible that my messages are not being delivered to the list?


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Comment By: Alexander Belopolsky (belopolsky)
Date: 2007-03-23 19:44

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I've fixed the flaws in star-star-mapping-1.patch .  I will ask on
python-dev about the feature.  If the proposal is accepted, I will probably
refactor the code to avoid using the second goto label.
File Added: star-star-mapping-1.patch

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Comment By: Georg Brandl (gbrandl)
Date: 2007-03-23 18:45

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Two flaws:
- what if kwdict is NULL? Shouldn't happen, but the old version raises an
error in this case.
- if PyDict_Update fails, tmpdict is leaked.

Please ask on python-dev whether to include this feature.

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