In Python, how to check if a string only contains certain characters?

Question

In Python, how to check if a string only contains certain characters?

I need to check a string containing only a..z, 0..9, and . (period) and no other character.

Answer 1

A different approach, because in my case I needed to also check whether it contained certain words (like 'test' in this example), not characters alone:

input_string = 'abc test'
input_string_test = input_string
allowed_list = ['a', 'b', 'c', 'test', ' ']

for allowed_list_item in allowed_list:
    input_string_test = input_string_test.replace(allowed_list_item, '')

if not input_string_test:
    # test passed

So, the allowed strings (char or word) are cut from the input string. If the input string only contained strings that were allowed, it should leave an empty string and therefore should pass if not input_string.