# chemicalFormulas.py # # Copyright (c) 2003, Paul McGuire # from pyparsing import Word, Optional, OneOrMore, Group, ParseException, Regex 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 digits = "0123456789" # Version 1 element = Regex("A[cglmrstu]|B[aehikr]?|C[adeflmorsu]?|D[bsy]|" "E[rsu]|F[emr]?|G[ade]|H[efgos]?|I[nr]?|Kr?|L[airu]|" "M[dgnot]|N[abdeiop]?|Os?|P[abdmortu]?|R[abefghnu]|" "S[bcegimnr]?|T[abcehilm]|Uu[bhopqst]|U|V|W|Xe|Yb?|Z[nr]") elementRef = Group( element + Optional( Word( digits ), default="1" ) ) formula = OneOrMore( elementRef ) fn = lambda elemList : sum( [ atomicWeight[elem]*int(qty) for elem,qty in elemList ] ) test( formula, "H2O", fn ) test( formula, "C6H5OH", fn ) test( formula, "NaCl", fn ) print # Version 2 - access parsed items by field name 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 ) print # Version 3 - convert integers during parsing process integer = Word( digits ).setParseAction(lambda t:int(t[0])) elementRef = Group( element.setResultsName("symbol") + \ Optional( integer, default=1 ).setResultsName("qty") ) formula = OneOrMore( elementRef ) fn = lambda elemList : sum( [ atomicWeight[elem.symbol]*elem.qty for elem in elemList ] ) test( formula, "H2O", fn ) test( formula, "C6H5OH", fn ) test( formula, "NaCl", fn )