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From: Christian Heimes <christian@python.org>
Subject: Re: Python 3: dict & dict.keys()
Date: Wed, 24 Jul 2013 23:06:56 +0200
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Xref: csiph.com comp.lang.python:51167

Am 24.07.2013 18:34, schrieb Chris Angelico:
> Side point: Why is iterating over a dict equivalent to .keys() rather
> than .items()? It feels odd that, with both options viable, the
> implicit version iterates over half the dict instead of all of it.
> Obviously it can't be changed now, even if .items() were the better
> choice, but I'm curious as to the reason for the decision.

Consider this:

if key in dict:
    ...

for key in dict:
   ...

It would be rather surprising if "in" as containment checks operates on
keys and "in" as iterator returns (key, value) tuples.

Christian