Task: converting a string from camel case to snake case

Need to convert a string from camel case to snake case, add the ability to change the separator. I solved the problem, but would like to know which way is more correct to solve it.

def camel_to_snake(str, sep=' '):    snake_register = ''    for i in str:        if i.isupper():            snake_register += sep + i.lower()        else:            snake_register += i    print(snake_register.lstrip(sep))camel_register = 'ThisIsCamelCased'camel_to_snake(camel_regist