Python: return the index of the first element of a list which makes a passed function true

Question

The list.index(x) function returns the index in the list of the first item whose value is x.

Is there a function, list_func_index()

Answer 1

You could do that in a one-liner using generators:

next(i for i,v in enumerate(l) if is_odd(v))

The nice thing about generators is that they only compute up to the requested amount. So requesting the first two indices is (almost) just as easy:

y = (i for i,v in enumerate(l) if is_odd(v))
x1 = next(y)
x2 = next(y)

Though, expect a StopIteration exception after the last index (that is how generators work). This is also convenient in your "take-first" approach, to know that no such value was found --- the list.index() function would throw ValueError here.