python - 如何使用 pyparsing 验证 bool 表达式语法？

Question

我正在使用 Pyparsing 库来评估简单的 bool 查询，如下所示:

• (真与真)或假与真
• (真与(真或假或真))

使用示例部分中的 simpleBool 脚本 ( simpleBool.py )，我在尝试验证表达式语法时遇到了障碍。像下面这样的表达式被认为是有效的，即使它们有明显的语法问题:

• (真与真)或假与真或或
• (真与(真或假或真))((((

有人知道如何使用 Pyparsing 验证语法吗？

这是根据要求的测试脚本:

#
# 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
#
from pyparsing import infixNotation, opAssoc, Keyword, Word, alphas

# define classes to be built at parse time, as each matching
# expression type is parsed
class BoolOperand(object):
    def __init__(self,t):
        self.label = t[0]
        self.value = eval(t[0])
    def __bool__(self):
        return self.value
    def __str__(self):
        return self.label
    __repr__ = __str__
    __nonzero__ = __bool__

class BoolBinOp(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)) + ")"
    def __bool__(self):
        return self.evalop(bool(a) for a in self.args)
    __nonzero__ = __bool__
    __repr__ = __str__

class BoolAnd(BoolBinOp):
    reprsymbol = '&'
    evalop = all

class BoolOr(BoolBinOp):
    reprsymbol = '|'
    evalop = any

class BoolNot(object):
    def __init__(self,t):
        self.arg = t[0][1]
    def __bool__(self):
        v = bool(self.arg)
        return not v
    def __str__(self):
        return "~" + str(self.arg)
    __repr__ = __str__
    __nonzero__ = __bool__

TRUE = Keyword("True")
FALSE = Keyword("False")
boolOperand = TRUE | FALSE | Word(alphas,max=1)
boolOperand.setParseAction(BoolOperand)

# 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),
    ])


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 t,expected in tests:
        res = boolExpr.parseString(t)[0]
        success = "PASS" if bool(res) == expected else "FAIL"
        print (t,'\n', res, '=', bool(res),'\n', success, '\n')

Answer 1

@PaulMcGuire 的回答:

将 boolExpr.parseString(t)[0] 更改为 boolExpr.parseString(t, parseAll=True)[0]。如果 Pyparsing 可以在字符串的前导部分找到有效的匹配项，即使末尾添加了垃圾，也不会引发异常。通过添加 parseAll=True，您可以告诉 pyparsing 整个字符串必须成功解析。