On Sun, May 20, 2012 at 5:44 AM, pete McEvoy <peterx.mce...@gmail.com> wrote:
> I am confused by some of the dictionary setdefault behaviour, I think
> I am probably missing the obvious here.
>
> def someOtherFunct():
> print "in someOtherFunct"
> return 42
>
> x = myDict.setdefault(1, someOtherFunct()) # <<<<< I didn't
> expect someOtherFunct to get called here
Python doesn't have lazy evaluation as such, but if what you want is a
dictionary that calls a function of yours whenever a value isn't
found, check out collections.defaultdict:
>>> import collections
>>> a=collections.defaultdict()
>>> def func():
print("Generating a default!")
return 42
>>> a.default_factory=func
>>> x = a[1]
Generating a default!
>>> x = a[1]
Tested in 3.2, but should work fine in 2.5 and newer.
ChrisA
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