/usr/share/doc/python-pyparsing/examples/simpleBool.py is in python-pyparsing 1.5.2-2ubuntu1.
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# simpleBool.py
#
# Example of defining a boolean logic parser using
# the operatorGrammar helper method in pyparsing.
#
# In this example, parse actions associated with each
# operator expression will "compile" the expression
# into BoolOperand subclass objects, which can then
# later be evaluated for their boolean value.
#
# Copyright 2006, by Paul McGuire
#
from pyparsing import *
class BoolOperand(object):
def __init__(self,t):
self.args = t[0][0::2]
def __str__(self):
sep = " %s " % self.reprsymbol
return "(" + sep.join(map(str,self.args)) + ")"
class BoolAnd(BoolOperand):
reprsymbol = '&'
def __nonzero__(self):
for a in self.args:
if isinstance(a,basestring):
v = eval(a)
else:
v = bool(a)
if not v:
return False
return True
class BoolOr(BoolOperand):
reprsymbol = '|'
def __nonzero__(self):
for a in self.args:
if isinstance(a,basestring):
v = eval(a)
else:
v = bool(a)
if v:
return True
return False
class BoolNot(BoolOperand):
def __init__(self,t):
self.arg = t[0][1]
def __str__(self):
return "~" + str(self.arg)
def __nonzero__(self):
if isinstance(self.arg,basestring):
v = eval(self.arg)
else:
v = bool(self.arg)
return not v
boolOperand = Word(alphas,max=1) | oneOf("True False")
boolExpr = operatorPrecedence( boolOperand,
[
("not", 1, opAssoc.RIGHT, BoolNot),
("and", 2, opAssoc.LEFT, BoolAnd),
("or", 2, opAssoc.LEFT, BoolOr),
])
test = ["p and not q",
"not not p",
"not(p and q)",
"q or not p and r",
"q or not p or not r",
"q or not (p and r)",
"p or q or r",
"p or q or r and False",
"(p or q or r) and False",
]
p = True
q = False
r = True
print "p =", p
print "q =", q
print "r =", r
print
for t in test:
res = boolExpr.parseString(t)[0]
print t,'\n', res, '=', bool(res),'\n'
|