import re


def parse_mentions(input_str):
    """
    Parse '@mentions' out of a string, perform any formatting/munging
        and return a list of all we found.

    Args:
        input_str (str):    The string to parse.

    Returns:
        list:               List of all mentioned users.
    """

    # Seems reasonable to assume the mention will always happen at
    #   the beginning of the string, or have a space before.
    mention_re = re.compile(r'(\s@[a-zA-Z]+|^@[a-zA-Z]+)')

    mentions = mention_re.findall(input_str)

    return [m.replace('@', '').strip() for m in mentions]