# 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 )
|