def is_full_mxid(user_string):
if not user_string[<NUM_LIT:0>] == "<STR_LIT:@>":<EOL><INDENT>return False<EOL><DEDENT>parts = user_string[<NUM_LIT:1>:].split("<STR_LIT::>")<EOL>localpart_chars = ascii_lowercase + digits + "<STR_LIT>"<EOL>if not (len(parts) == <NUM_LIT:2> and all([i in localpart_chars for i in parts[<NUM_LIT:0>]])):<EOL><INDENT>return False<EOL><DEDENT>return True<EOL>
Returns True if a string is a valid mxid.