[Pyparsing] fourFn.py explanation and slight modification

Glenn Pierce

2014-09-04 10:00:18 UTC

Hmm I got it going with this

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( "/" )
lte = Literal( ">=" )
lt = Literal( "<" )
gt = Literal( ">" )
anding = CaselessLiteral( "and" )
oring = CaselessLiteral( "or" )
lpar = Literal( "(" ).suppress()
rpar = Literal( ")" ).suppress()
addop = plus | minus | lte | lt | gt
multop = mult | div
logicalop = anding | oring
expop = Literal( "^" )
pi = CaselessLiteral( "PI" )
expr = Forward()
atom = ((Optional(oneOf("- +")) +

(pi|e|fnumber|ident+lpar+expr+rpar).setParseAction(self.pushFirst))
| Optional(oneOf("- +")) + Group(lpar+expr+rpar)
).setParseAction(self.pushUMinus)
# by defining exponentiation as "atom [ ^ factor ]..." instead of
# "atom [ ^ atom ]...", we get right-to-left exponents, instead of
left-to-right
# that is, 2^3^2 = 2^(3^2), not (2^3)^2.
factor = Forward()
factor <<= atom + ZeroOrMore( ( expop + factor ).setParseAction(
self.pushFirst ) )
term = factor + ZeroOrMore( ( multop + factor ).setParseAction(
self.pushFirst ) )
term2 = term + ZeroOrMore( ( addop + term ).setParseAction(
self.pushFirst ) )
expr <<= term2 + ZeroOrMore( ( logicalop + term2 ).setParseAction(
self.pushFirst ) )

Can't say I 100% understand the grammer though. Any short explanations
would be great.

Post by Glenn Pierce
Hi I am new to pyparsing and I am having trouble understanding the grammer
of the example fourFn.py
<http://pyparsing.wikispaces.com/file/view/fourFn.py/30154950/fourFn.py>
I am trying to add comparison operators and logical operators to this
example. The comparisons work ok but I not sure how to add the logical
operators AND OR NOT
So far I have this
plus = Literal( "+" )
minus = Literal( "-" )
mult = Literal( "*" )
div = Literal( "/" )
lte = Literal( ">=" )
lt = Literal( "<" )
gt = Literal( ">" )
anding = CaselessLiteral( "and" )
lpar = Literal( "(" ).suppress()
rpar = Literal( ")" ).suppress()
addop = plus | minus | lte | lt | gt
multop = mult | div
expop = Literal( "^" )
pi = CaselessLiteral( "PI" )
sensor_values = CaselessLiteral( "sensor_values" )
expr = Forward()
atom = ((Optional(oneOf("- +")) +
(sensor_values|pi|e|fnumber|ident+lpar+expr+rpar).setParseAction(self.pushFirst))
| Optional(oneOf("- +")) + Group(lpar+expr+rpar)
).setParseAction(self.pushUMinus)
# by defining exponentiation as "atom [ ^ factor ]..." instead of
# "atom [ ^ atom ]...", we get right-to-left exponents, instead of
left-to-right
# that is, 2^3^2 = 2^(3^2), not (2^3)^2.
factor = Forward()
factor <<= atom + ZeroOrMore( ( expop + factor ).setParseAction(
self.pushFirst ) )
term = factor + ZeroOrMore( ( multop + factor ).setParseAction(
self.pushFirst ) )
expr <<= term + ZeroOrMore( ( addop + term ).setParseAction(
self.pushFirst ) )
Could someone perhaps explain the three lines below and how I would add my
CaselessLiteral( "and" ) boolean
so I could do something like
nsp.eval('10 >= 5 AND 10 < 15')
factor <<= atom + ZeroOrMore( ( expop + factor ).setParseAction(
self.pushFirst ) )
term = factor + ZeroOrMore( ( multop + factor ).setParseAction(
self.pushFirst ) )
expr <<= term + ZeroOrMore( ( addop + term ).setParseAction(
self.pushFirst ) )
PS what is the <<= operator ? I can't find the docs for it
Thanks for any help.