This patch adds an optional default value to dict.pop,
so that it parallels dict.get, see discussion in bug
639806.

If no default is given, the old behavior still exists,
so backwards compatibility is no problem.
The new pop must use METH_VARARGS
and PyArg_UnpackTuple, somewhat effecting
efficiency.

If this is considered desirable, I could also
provide the same behavior for list.pop.

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The patch looks fine.  Assigning to Guido for 
pronouncement.

Guido, the patch adds optional get() like functionality for 
dict.pop().  The nearest parallel is the default argument for 
getattr(obj, attr, [default]).  On the plus side, it makes pop 
easier to use and more flexible.  On the minus side, it adds 
more complexity to the mapping interface and it slows 
down the normal case for d.pop(k).

If it is accepted the poster should add test cases, a NEWS 
item, doc updates, and parallel changes to 
UserDict.UserDict and UserDict.DictMixin.  Then, re-assign 
to me and I'll check it all and apply it.

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Alex Martelli's argument convinced me, I'm +0.5 on the
feature. The 0.5 is because it's definitely feature bloat.
Given how few use cases there are for dict.pop() in the
first place, I'm not worried about the minor slowdown due to
extra argument parsing.

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dicts have a .pop() method?  Heh.  I must have slept 
through that one <wink>.

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Should I make a new NEWS item, or should
I modify the existing NEWS item about dict.pop?

And should I make a new whatsnew23 item or
modify the existing one?

I'm guessing a new NEWS item and a modified
whatsnew item, but I'll post a patch when you tell me.

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For NEWS, add a new entry (so that it documents a 
difference from Py2.3a2).

For whatsnew23, modify the existing entry (since it is a 
delta from Py2.3).

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You don't need to update whatsnew23.tex; its editor prefers
to do this himself.

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Okay, here's patchpop2 with the diff'ed dictobject,
UserDict, test_types, test_userdict, NEWS, and
Doc/lib/libstdtypes.  whew.

Let me know if you need any changes.
The change to DictMixin seems a bit
clumsy, but I liked it better than other things
I came up with.

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argh... I put the NEWS item in the wrong place.
Ignore patchpop2(I can't delete it), look at patchpop3.

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Misc/NEWS 1.69
Objects/dictobject.c 2.141
Doc/lib/libstdtypes.tex 1.120
Lib/UserDict.py 1.24
Lib/test/test_types.py 1.47
Lib/test/test_userdict.py 1.13

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Thanks for fixing up my UserDict.DictMixin patch.
Much nicer.