On Thu, 18 Dec 2008 09:51:01 -0500, Neal Becker <ndbeck...@gmail.com> wrote:
Tino Wildenhain wrote:
Neal Becker wrote:
...
So if __str__ is "meant for human eyes", then why isn't print using it!
it is:
> print x
str
but dict just uses repr() for all its childs to print.
T.
That makes no sense to me. If I call 'print' on a container, why
wouldn't it recursively print on the contained objects? Since print
means call str, printing a container should recursively call str on the
objects.
Every class is free on how to best implement __str__, you will find
the same behavior on tuple and list as well.
Maybe its discussable to change the implementation sensibly, best if you
would come with a proposal? Perhaps pprint.pprint is a starting point?
Regards
Tino
First, I'd like to know if there is a rationale for the current design. Am I
correct in thinking this is a defect?
There is a rationale. Consider:
>>> class strit(object):
... def __init__(self, it):
... self.it = it
... def __repr__(self):
... return str(self.it)
...
This will let us see what a dict.__str__ which called __str__ on the objects
in it would look like. So first, something simple:
>>> print str({strit("['foo']"): 'bar'})
{['foo']: 'bar'}
>>>
Mildly confusing - you can't use a list as a dict key! But it could be
worse:
>>> print str({strit("1: 2, 3"): 'bar'})
{1: 2, 3: 'bar'}
>>>
Wait - *how* many items are in that dictionary?
Hopefully that makes the rationale clear - when a human is looking at the
str of a dict (and a human is ostensibly the intended audience) - using
the __repr__ of the contained objects makes it easier for the human to
understand what's in the dict. Using __str__ would make it much harder
in many cases.
Jean-Paul
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