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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 BoolXXX class instances, which can then
# later be evaluated for their boolean value.
#
# Copyright 2006, by Paul McGuire
# Updated 2013-Sep-14 - improved Python 2/3 cross-compatibility
# Updated 2021-Sep-27 - removed Py2 compat; added type annotations
#
from typing import Callable, Iterable
from pyparsing import infixNotation, opAssoc, Keyword, Word, alphas, ParserElement
ParserElement.enablePackrat()
# define classes to be built at parse time, as each matching
# expression type is parsed
class BoolOperand:
def __init__(self, t):
self.label = t[0]
self.value = eval(t[0])
def __bool__(self) -> bool:
return self.value
def __str__(self) -> str:
return self.label
__repr__ = __str__
class BoolNot:
def __init__(self, t):
self.arg = t[0][1]
def __bool__(self) -> bool:
v = bool(self.arg)
return not v
def __str__(self) -> str:
return "~" + str(self.arg)
__repr__ = __str__
class BoolBinOp:
repr_symbol: str = ""
eval_fn: Callable[
[Iterable[bool]], bool
] = lambda _: False
def __init__(self, t):
self.args = t[0][0::2]
def __str__(self) -> str:
sep = " %s " % self.repr_symbol
return "(" + sep.join(map(str, self.args)) + ")"
def __bool__(self) -> bool:
return self.eval_fn(bool(a) for a in self.args)
class BoolAnd(BoolBinOp):
repr_symbol = "&"
eval_fn = all
class BoolOr(BoolBinOp):
repr_symbol = "|"
eval_fn = any
# define keywords and simple infix notation grammar for boolean
# expressions
TRUE = Keyword("True")
FALSE = Keyword("False")
NOT = Keyword("not")
AND = Keyword("and")
OR = Keyword("or")
boolOperand = TRUE | FALSE | Word(alphas, max=1)
boolOperand.setParseAction(BoolOperand).setName("bool_operand")
# define expression, based on expression operand and
# list of operations in precedence order
boolExpr = infixNotation(
boolOperand,
[
(NOT, 1, opAssoc.RIGHT, BoolNot),
(AND, 2, opAssoc.LEFT, BoolAnd),
(OR, 2, opAssoc.LEFT, BoolOr),
],
).setName("boolean_expression")
if __name__ == "__main__":
p = True
q = False
r = True
tests = [
("p", True),
("q", False),
("p and q", False),
("p and not q", True),
("not not p", True),
("not(p and q)", True),
("q or not p and r", False),
("q or not p or not r", False),
("q or not (p and r)", False),
("p or q or r", True),
("p or q or r and False", True),
("(p or q or r) and False", False),
]
print("p =", p)
print("q =", q)
print("r =", r)
print()
for test_string, expected in tests:
res = boolExpr.parseString(test_string)[0]
success = "PASS" if bool(res) == expected else "FAIL"
print(test_string, "\n", res, "=", bool(res), "\n", success, "\n")