what does find do in python code example

Example: find in python

def find_all_indexes(input_str, search_str):
    l1 = []
    length = len(input_str)
    index = 0
    while index < length:
        i = input_str.find(search_str, index)
        if i == -1:
            return l1
        l1.append(i)
        index = i + 1
    return l1


s = 'abaacdaa12aa2'
print(find_all_indexes(s, 'a'))
print(find_all_indexes(s, 'aa'))