def rotate(self, atom):
        """(atom)->start the cycle at position atom, assumes
        that atom is in the cycle"""
        try:
            index = self.atoms.index(atom)
        except ValueError:
            raise CycleError("atom %s not in cycle"%(atom))

        self.atoms = self.atoms[index:] + self.atoms[:index]
        self.bonds = self.bonds[index:] + self.bonds[:index]
def rotate ( self , atom ) : try : index = self . atoms . index ( atom ) except ValueError : raise CycleError ( "atom %s not in cycle" % ( atom ) ) self . atoms = self . atoms [ index : ] + self . atoms [ : index ] self . bonds = self . bonds [ index : ] + self . bonds [ : index ]
(atom)->start the cycle at position atom, assumes
        that atom is in the cycle