Python, string,

Program to join a list of strings with a given separator

def join(separator: str, separated: list[str]) -> str:
    >>> join("", ["a", "b", "c", "d"])
    >>> join("#", ["a", "b", "c", "d"])
    >>> join("#", "a")
    >>> join(" ", ["You", "are", "amazing!"])
    'You are amazing!'
    >>> join("#", ["a", "b", "c", 1])
    Traceback (most recent call last):
    Exception: join() accepts only strings to be joined
    joined = ""
    for word_or_phrase in separated:
        if not isinstance(word_or_phrase, str):
            raise Exception("join() accepts only strings to be joined")
        joined += word_or_phrase + separator
    return joined.strip(separator)

if __name__ == "__main__":
    from doctest import testmod