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# chemicalFormulas.py
#
# Copyright (c) 2003, Paul McGuire
#
from pyparsing import Word, Optional, OneOrMore, Group, ParseException, Regex
from pyparsing import alphas
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 ), end=' ')
except ParseException as 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]|U(u[bhopqst])?|V|W|Xe|Yb?|Z[nr]")
element = Word( alphas.upper(), alphas.lower(), max=2)
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("symbol") + Optional( Word( digits ), default="1" )("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("symbol") + Optional( integer, default=1 )("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 )
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