Implements dict.sequpdate() as discussed on python-
dev:

def sequpdate(self, iterable, value=True):
    for k in iterable:
        self[k] = value
    return self

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I see no reason why d.sequpdate() should return self.
d.update() doesn't either.

Also, as I suggested on python-dev, a fromseq() constructor
(as a class method) would be nice:

  >>> dict.fromseq('End Quit Stop Abort'.split())
  {'End': True, 'Quit': True, 'Stop': True, 'Abort': True}
  >>>

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One more thing: I'd say the default value should be None.
This makes the idiom also useful to initialize dicts which
later get filled with proper values. This doesn't take
anything away from your original use case.

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Attached revised patch incorporating all of the review 
comments.  Changed default to None.  Made a static 
method instead of a classmethod because cls was not 
used.  Doesn't return self.

Tests, docs, and news item revised accordingly.

Ready for BDFL pronouncement.

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Hm, but the convention for "alternate constructors" is that
the cls argument *is* used to determine the type of the new
instance. This way, the constructors are inherited in a
meaningful way by subclasses of dict.

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Done!  Revise patch attached.

It is now a class method and uses cls for the type of the 
new instance.  Added tests to demonstrate meaningful 
inheritance.

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It seems the code and the docs are out of sync in 
fromseq2.diff.

The docs say "fromseq(sequence, value=True)" while the 
code does "fromseq(sequence, value=None)"

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Fixed news item.

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- I'm not sure whether PyObject_CallObject() is the right
idiom here. I would have expected to call cls->tp_new (if
not NULL), but I'm not sure either way.
- I would get rid of the loop counter: you're not using it.
for (;;) will do nicely
- you're XDECREF'ing values of which you know they're not NULL
- idem XINCREF. Also: I'm pretty sure you should incref d at
the end: I think it currently leaks.

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dang, that should've read "you should NOT incref d at the end".

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Okay, fixed decrefs, eliminated i; used for(;;).
Left in PyObject_CallObject because it's clean.
Thanks.

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Btw. I was looking for more info on METH_CLASS and came
across this thread on python-dev:
 
http://mail.python.org/pipermail/python-dev/2002-April/023566.html
which resulted in this bug report:
  http://www.python.org/sf/548651
which has not been resolve. I'll add a comment there, too.

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I'm ok with this, but I haven't had time to review the code.

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After more code review, added PyDict_Check.

Also, discussion on python-dev showed a need to rename 
the method to indicate that keys were being used rather 
than items.  The sequence part of the name was dropped 
because any iterable will do as an argument.

Checked-in as:
Misc/NEWS 1.548
Objects/dictobject.c 2.132
Lib/test/test_types.py 1.41
Doc/lib/libstdtypes.tex 1.111