def coerce(cls, string):
        """Create a :class:`Requirement` object from a given package spec."""
        match = re.match(cls.spec_regex, string)
        if not match:
            raise InvalidRequirementSpecError("could not parse requirement")
        package = match.group(1)
        if all(match.group(2, 3)):
            version = "".join(match.group(2, 3))
        else:
            version = None
        return cls(package, version)
def __exit__(self, exc_type, exc_value, traceback):
        connection = get_connection(self.using)
        try:
            self._no_monkey.__exit__(self, exc_type, exc_value, traceback)
        except DatabaseError:
            transaction_states[self.using].rollback()
        else:
            if not connection.closed_in_transaction and exc_type is None and \
                    not connection.needs_rollback:
                if transaction_states[self.using]:
                    transaction_states[self.using].commit()
            else:
                transaction_states[self.using].rollback()