# chemicalFormulas.py # # Copyright (c) 2003, Paul McGuire # from pyparsing import Word, Optional, OneOrMore, Group, ParseException atomicWeight = { "O" : 15.9994, "H" : 1.00794, "Na" : 22.9897, "Cl" : 35.4527, "C" : 12.0107 } def test( bnf, strg, fn=None ): try: print strg,"->", bnf.parseString( strg ), except ParseException, pe: print pe else: if fn != None: print fn( bnf.parseString( strg ) ) else: print caps = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" lowers = caps.lower() digits = "0123456789" element = Word( caps, lowers ) elementRef = Group( element + Optional( Word( digits ), default="1" ) ) formula = OneOrMore( elementRef ) fn = lambda x : "(" + str(sum( [ atomicWeight[elem]*int(qty) for elem,qty in x ] ) ) + ")" test( formula, "H2O", fn ) test( formula, "C6H5OH", fn ) test( formula, "NaCl", fn ) element = Word( caps, lowers ) elementRef = Group( element.setResultsName("symbol") + \ Optional( Word( digits ), default="1" ).setResultsName("qty") ) formula = OneOrMore( elementRef ) fn = lambda elemList : sum( [ atomicWeight[elem.symbol]*int(elem.qty) for elem in elemList ] ) test( formula, "H2O", fn ) test( formula, "C6H5OH", fn ) test( formula, "NaCl", fn )