Find matching index Finds the index of the first element in the given list that satisfies the provided testing function. Use a list comprehension, enumerate() and next() to return the index of the first element in lst for which fn returns True. def find_index(lst, fn): return next(i for i, x in enumerate(lst) if fn(x)) find_index([1, 2, 3, 4], lambda n: n % 2 == 1) # 0