Torsten Mohr <tm...@s.netic.de> wrote:
> how is the rule in Python, if i pass objects to a function, when is this
> done by reference and when is it by value?
>
> def f1(a):
> a = 7
>
> b = 3
> f1(b)
> print b
>=> 3
>
> Integers are obviously passed by value, lists and dicts by reference.
>
> Is there a general rule? Some common formulation?
Yes, integers are 'obviously' passed by value, except that if they were you
couldn't do this:
>>> x = 26*1000
>>> y = 26000
>>> id(x)==id(y)
False
>>> def whichint(arg):
if id(arg)==id(x):
print "You passed x"
elif id(arg)==id(y):
print "You passed y"
>>> whichint(x)
You passed x
>>> whichint(y)
You passed y
The general rule is that everything is passed in exactly the same way.
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