itertools.takewhile() returns an iterator that generates elements from an iterable as long as a given predicate function evaluates to True.

import itertools

nums = [1, 61, 7, 9, 2077]

print(list(itertools.takewhile(lambda x: x < 100, nums)))

# [1, 61, 7, 9]

This function is different from the built-in filter() function.

The filter function will go through the whole list:

nums = [1, 61, 7, 9, 2077]

print(list(filter(lambda x: x < 10, nums)))

# [1, 7, 9]

However, the itertools.takewhile function, as its name implies, will stop when the evaluating function is False:

import itertools

nums = [1, 61, 7, 9, 2077]

print(list(itertools.takewhile(lambda x: x < 10, nums)))

# [1]