from openbabel import openbabel

mol = openbabel.OBMol()
print(mol.NumAtoms()) #Should print 0 (atoms)

a = mol.NewAtom()
a.SetAtomicNum(6)   # carbon atom
a.SetVector(0.0, 1.0, 2.0) # coordinates

b = mol.NewAtom()
mol.AddBond(1, 2, 1)   # atoms indexed from 1
print(mol.NumAtoms()) #Should print 2 (atoms)
print(mol.NumBonds()) 

mol.Clear();