mol_class.py

############################################
def read_mols(fname):
        mol = molecule('Water')
        for line in fname:
                ats,x,y,z=line.split()
                at=atom(ats,float(x),float(y),float(z))
                mol.addatom(at)
        return(mol)
############################################
class atom:
        def __init__(self,atno,x,y,z):
                self.atno = atno
                self.position = (x,y,z)
        def symbol(self):   # a class method
                return Atno_to_Symbol[atno]
        def __repr__(self): # overloads printing
                return '%s %10.4f %10.4f %10.4f' %(self.atno, self.position[0],
                         self.position[1],self.position[2])
############################################
class molecule:
        def __init__(self,name='Generic'):
                self.name = name
                self.atomlist = []
        def addatom(self,atom):
                self.atomlist.append(atom)
        def __repr__(self):
                str = ' %d \n' % len(self.atomlist)
                str = str +'This is a molecule named %s\n' % self.name
                for atom in self.atomlist:
                        str = str + `atom` + '\n'
                return str
############################################

hi,
are you understand this str = str + atom + '\n'?