New submission from Łukasz Langa luk...@langa.pl:
Currently the constructor in defaultdict only accepts factories. It would be
very handy to allow for concrete values as well. It's implementable either by
checking if the argument is callable or by a new keyword argument.
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assignee:
Michael Foord mich...@voidspace.org.uk added the comment:
I would love this functionality (I almost always initialise defaultdict with a
lambda that just returns a concrete value).
Unfortunately it seems like adding a keyword argument isn't possible because
defaultdict takes arbitrary keyword
Eric Smith e...@trueblade.com added the comment:
-1 from me. You can't use keywords, and if you make the value callable at a
later date then suddenly you'll change the behavior of seemingly unrelated
code. Is a lambda so bad?
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nosy: +eric.smith
Łukasz Langa luk...@langa.pl added the comment:
Both arguments are true and definitive. Last possibility would be to introduce
a factory function for defaultdicts that would only accept concrete values:
from collections import fallbackdict
Then this factory could produce defaultdict
Eric Smith e...@trueblade.com added the comment:
How about:
from collections import defaultdict
class defaultdict_value(defaultdict):
def __init__(self, value):
defaultdict.__init__(self, lambda : value)
x = defaultdict_value(3)
print(x[1])
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Steve Holden st...@holdenweb.com added the comment:
On 11/25/2010 11:48 AM, Eric Smith wrote:
Eric Smith e...@trueblade.com added the comment:
How about:
from collections import defaultdict
class defaultdict_value(defaultdict):
def __init__(self, value):
Éric Araujo mer...@netwok.org added the comment:
Like three-liners? whatsnew/2.5 gives us this one:
class zerodict(dict):
def __missing__(self, key):
return 0
I don’t think it’s too painful to have to use defaultdict with a lambda. We
can’t use a keyword argument and I’m -0.5 on
Changes by Raymond Hettinger rhettin...@users.sourceforge.net:
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assignee: lukasz.langa - rhettinger
nosy: +rhettinger
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Python tracker rep...@bugs.python.org
http://bugs.python.org/issue10533
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Raymond Hettinger rhettin...@users.sourceforge.net added the comment:
It would be very handy to allow for concrete values as well.
Do you have use cases for a concrete integer value that isn't zero?
Since we can currently use defaultdict(int) or defaultdict(tuple), is the
purpose just to
Łukasz Langa luk...@langa.pl added the comment:
A couple of points:
1. Eric's proposal is what I had in mind with the `fallbackdict' idea.
2. I'm also reluctant to add more variants to the standard library. Then again
if it contained a `fallbackdict' I wouldn't probably ever use `defaultdict'
Steve Holden st...@holdenweb.com added the comment:
On 11/25/2010 1:44 PM, Łukasz Langa wrote:
To sum up: if you don't find the idea of adding `fallbackdict'
(possibly with an different *short* name) worth it, then I'm +1 on
correcting the docs in terms of __missing__ and leaving the
Alex alex.gay...@gmail.com added the comment:
I agree with Łukasz, it's more clutter than is worth for what amounts to:
fallbackdict = lambda c, **kwargs: defaultdict(lambda c, **kwargs)
I will note, however, that almost all my use cases are with factories,
primarily list set or int, and it
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