Object is enumerable but not indexable?

Python only allows these things if the class has methods for them:

• __getitem__ is required for the [] syntax.
• __iter__ and __next__¹ are required to iterate.

Any class can define one without defining the other. __getattr__ is usually not defined if it would be inefficient.

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¹__next__ is required on the class returned by __iter__.

This is a result of foo being iterable, but not having a __getitem__ function. You can use itertools.isslice to get the nth element of an iterable like so

import itertools

def nth(iterable, n, default=None):
    "Returns the nth item or a default value"
    return next(itertools.islice(iterable, n, None), default)