import openbabel

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

a = mol.NewAtom()
b = mol.NewAtom()
mol.AddBond(1, 2, 1)
print 'Should print 2 (atoms)'
print mol.NumAtoms()
print 'Should print 1 (bond)'
print mol.NumBonds()

obConversion = openbabel.OBConversion()
obConversion.SetInAndOutFormats("smi", "mdl")

mol.Clear()
obConversion.ReadString(mol, "C1=CC=CS1")

print 'Should print 5 (atoms)'
print mol.NumAtoms()

mol.AddHydrogens()
print 'Should print 9 (atoms) after adding hydrogens'
print mol.NumAtoms()

outMDL = obConversion.WriteString(mol)

obConversion.WriteFile(mol, 'temp.mdl')