def main():
   SmilesString1 = sys.argv[1]
   SmilesString2 = sys.argv[2]
   print SmilesString1, SmilesString2

   mw1 = float(tca.molecularMass(SmilesString1))
   mw2 = float(tca.molecularMass(SmilesString2))

   print mw1, mw2, math.fabs(mw1-mw2)

   

   formula1 = tca.MolecularFormula(SmilesString1)
   formula2 = tca.MolecularFormula(SmilesString2)
   val = tca.compareFormula(formula1,formula2)
    # for ligand1
    # cheek if smiles is in dictionary has already be gotten
    if (lig1 in lig_smiles):
        smiles1 = lig_smiles[lig1]
    else:  # if not know then get it.
        smiles1 = spfl.scrape_pdb_for_lig_smiles(lig1)
        if (smiles1 == ''):
            continue
        lig_smiles[lig1] = smiles1
        fileout2.write(smiles1 + ' ' + lig1 + '\n')

    if (lig1 in lig_formula):
        formula1 = lig_formula[lig1]
    else:
        formula1 = tancal.MolecularFormula(smiles1)
        lig_formula[lig1] = formula1
        fileout3.write(formula1 + ' ' + lig1 + '\n')

    if (lig1 in lig_mw):
        mw1 = lig_mw[lig1]
    else:
        mw1 = float(tancal.molecularMass(smiles1))
        lig_mw[lig1] = mw1

    # for ligand2
    if (lig2 in lig_smiles):
        smiles2 = lig_smiles[lig2]
    else:
        smiles2 = spfl.scrape_pdb_for_lig_smiles(lig2)
        if (smiles2 == ''):