def __parser(expression):
        """ adopted from Paul McGuire example. http://pyparsing.wikispaces.com/file/view/fourFn.py
        """
        expr_stack = []

        def push_first(strg, loc, toks):
            expr_stack.append(toks[0])

        def push_u_minus(strg, loc, toks):
            if toks and toks[0] == '-':
                expr_stack.append('unary -')

        point = Literal('.')
        _e = CaselessLiteral('E')
        fnumber = Combine(Word('+-' + nums, nums) +
                          Optional(point + Optional(Word(nums))) +
                          Optional(_e + Word('+-' + nums, nums)))
        ident = Word(alphas, alphas + nums + '_$')

        plus = Literal("+")
        minus = Literal("-")
        mult = Literal("*")
        div = Literal("/")
        lpar = Literal("(").suppress()
        rpar = Literal(")").suppress()
        addop = plus | minus
        multop = mult | div
        expop = Literal("^")
        _pi = CaselessLiteral("PI")
        x = CaselessLiteral("X")

        expr = Forward()
        atom = (Optional("-") + (x | _pi | _e | fnumber | ident + lpar + expr + rpar).setParseAction(push_first) |
                (lpar + expr.suppress() + rpar)).setParseAction(push_u_minus)

        factor = Forward()
        factor << atom + ZeroOrMore((expop + factor).setParseAction(push_first))

        term = factor + ZeroOrMore((multop + factor).setParseAction(push_first))
        expr << term + ZeroOrMore((addop + term).setParseAction(push_first))

        expr.parseString(expression)
        return expr_stack
def __parser(expression):
        """ adopted from Paul McGuire example. http://pyparsing.wikispaces.com/file/view/fourFn.py
        """
        expr_stack = []

        def push_first(strg, loc, toks):
            expr_stack.append(toks[0])

        def push_u_minus(strg, loc, toks):
            if toks and toks[0] == '-':
                expr_stack.append('unary -')

        point = Literal('.')
        _e = CaselessLiteral('E')
        fnumber = Combine(Word('+-' + nums, nums) +
                          Optional(point + Optional(Word(nums))) +
                          Optional(_e + Word('+-' + nums, nums)))
        ident = Word(alphas, alphas + nums + '_$')

        plus = Literal("+")
        minus = Literal("-")
        mult = Literal("*")
        div = Literal("/")
        lpar = Literal("(").suppress()
        rpar = Literal(")").suppress()
        addop = plus | minus
        multop = mult | div
        expop = Literal("^")
        _pi = CaselessLiteral("PI")
        x = CaselessLiteral("X")

        expr = Forward()
        atom = (Optional("-") + (x | _pi | _e | fnumber | ident + lpar + expr + rpar).setParseAction(push_first) |
                (lpar + expr.suppress() + rpar)).setParseAction(push_u_minus)

        factor = Forward()
        factor << atom + ZeroOrMore((expop + factor).setParseAction(push_first))

        term = factor + ZeroOrMore((multop + factor).setParseAction(push_first))
        expr << term + ZeroOrMore((addop + term).setParseAction(push_first))

        expr.parseString(expression)
        return expr_stack
def __parser ( expression ) : expr_stack = [ ] def push_first ( strg , loc , toks ) : expr_stack . append ( toks [ 0 ] ) def push_u_minus ( strg , loc , toks ) : if toks and toks [ 0 ] == '-' : expr_stack . append ( 'unary -' ) point = Literal ( '.' ) _e = CaselessLiteral ( 'E' ) fnumber = Combine ( Word ( '+-' + nums , nums ) + Optional ( point + Optional ( Word ( nums ) ) ) + Optional ( _e + Word ( '+-' + nums , nums ) ) ) ident = Word ( alphas , alphas + nums + '_$' ) plus = Literal ( "+" ) minus = Literal ( "-" ) mult = Literal ( "*" ) div = Literal ( "/" ) lpar = Literal ( "(" ) . suppress ( ) rpar = Literal ( ")" ) . suppress ( ) addop = plus | minus multop = mult | div expop = Literal ( "^" ) _pi = CaselessLiteral ( "PI" ) x = CaselessLiteral ( "X" ) expr = Forward ( ) atom = ( Optional ( "-" ) + ( x | _pi | _e | fnumber | ident + lpar + expr + rpar ) . setParseAction ( push_first ) | ( lpar + expr . suppress ( ) + rpar ) ) . setParseAction ( push_u_minus ) factor = Forward ( ) factor << atom + ZeroOrMore ( ( expop + factor ) . setParseAction ( push_first ) ) term = factor + ZeroOrMore ( ( multop + factor ) . setParseAction ( push_first ) ) expr << term + ZeroOrMore ( ( addop + term ) . setParseAction ( push_first ) ) expr . parseString ( expression ) return expr_stack
adopted from Paul McGuire example. http://pyparsing.wikispaces.com/file/view/fourFn.py
adopted from Paul McGuire example . http : // pyparsing . wikispaces . com / file / view / fourFn . py