IndexError and for x in list

[Niels Diepeveen]

"Michal Wallace (sabren)" schreef:
>     def _toStringKey(self, key):
>         """Convert numeric keys into string keys. Leaves string keys as is"""
>         # handle numeric keys:
>         if _isNum(key):
>             if not (0 <= key < len(self.idx)):
>                 ## oddly enough, it is this IndexError here
>                 ## that allows you to do "for x in myIdxDict:"
>                 raise IndexError, `key` + " is out of bounds."
>             # convert it to a string key
>             key = self.idx[key]
> 
>         return key

Or, a bit simpler:
    def _toStringKey(self, key):
        """Convert numeric keys into string keys. Leaves string keys as
is"""
        # note that sequence indexes must be integers
        if type(key) is type(0):   # note that sequence indexes must be
integers
            return self.idx[key]   # this will raise the IndexError when
needed
        else:
            return key

> Basically, I don't want to rely on an undocumented feature that could
> go away sometime. Is IndexError the right way to simulate a list?

If you take the above approach, that problem will go away, since you
will simply pass on the error handling of a real list, whatever that may
be. To be on the safe side, you might also implement __len__ if that
isn't already done. That should take care of any alternative
implementation of 'for' that I can imagine. If you really want to do
everything a list can do, read 'Emulating sequence and mapping types' in
the language reference.

-- 
Niels Diepeveen
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