How does "for" work?

[Aahz Maruch]

In article <Pine.SOL.3.96.1001010105911.8470C-100000 at condor.ee.washington.edu>,
Steve Juranich  <sjuranic at condor.ee.washington.edu> wrote:
>
>In the list object, I have overridden __getitem__ to be the following:
>
>def __getitem__(self, key):
>    return self.data[key]

Try this:

def __getitem__(self, key):
    if not self.data.has_key[key]: 
        raise IndexError
    return self.data[key]

The problem is that "for" wants an IndexError, not a KeyError.  An
alternate implementation that's a bit faster (at the expense of some
clarity if one is not thinking Pythonically):

def __getitem__(self, key):
    try:
        return self.data[key]
    except KeyError:
        raise IndexError
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