def generateChecker(self, argstring):
        """
        This checker factory expects to get a list of
        username:password pairs, with each pair also separated by a
        colon. For example, the string 'alice:f:bob:g' would generate
        two users, one named 'alice' and one named 'bob'.
        """
        checker = InMemoryUsernamePasswordDatabaseDontUse()
        if argstring:
            pieces = argstring.split(':')
            if len(pieces) % 2:
                from twisted.cred.strcred import InvalidAuthArgumentString
                raise InvalidAuthArgumentString(
                    "argstring must be in format U:P:...")
            for i in range(0, len(pieces), 2):
                username, password = pieces[i], pieces[i+1]
                checker.addUser(username, password)
        return checker

        This checker factory expects to get a list of
        username:password pairs, with each pair also separated by a
        colon. For example, the string 'alice:f:bob:g' would generate
        two users, one named 'alice' and one named 'bob'.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/plugins/cred_memory.py