enumerate

Say you want to loop over an iterable, but you want to keep an index of your position.

The most obvious way to do this is to use a separate counter variable, like so:

aseq = 'hello'
i = 0
for c in aseq:
    ....
    i += 1

While that will work, the cooler way is to use enumerate. Enumerate encapsulates any iterable in another iterable that will return the value as yielded by the inner iterable with the value of the current index.

aseq = 'hello'
for (i, c) in enumerate(aseq):
    ....