How does "for" work?

[Steve Juranich]

I have an object that is actually just a list of other, smaller items.

In the list object, I have overridden __getitem__ to be the following:

def __getitem__(self, key):
    return self.data[key]

This should be straightforward enough.  But when I try something like:

for item in list:
	# Whatever

I get a complaint once the for loop gets to the end of the list about a
KeyError.  The length of the list is 5176 (in this case going from 0-5175).
But the for loop tries to get list[5176].  Why does this happen?  How does
"for" know how long the list is?  Is the problem in my __len__ function or
in my __getitem__ function?  If I just change __getitem__ to return the
key-1th entry of the list, will that fix it?


BTW, I should mention that __len__() for the list looks like this:

def __len__(self):
    return len(self.data)

Where data is a dictionary of the smaller items, with a time index (by ints) 
being used as the key.

Thanks so much for the help.

----------------------------------------------------------------------
Stephen W. Juranich                         sjuranic at ee.washington.edu
Electrical Engineering         http://students.washington.edu/sjuranic
University of Washington             http://rcs.ee.washington.edu/ssli