def METHOD_NAME(self, atom):
    """Return the atom on the other end of this bond with respect to *atom*. *atom* has to be one of the atoms forming this bond, otherwise an exception is raised.
    """
    if atom is self.atom1:
        return self.atom2
    elif atom is self.atom2:
        return self.atom1
    else:
        raise MoleculeError('Bond.other_end: invalid atom passed')