rnetonet · April 22, 2024 16:52 · Sep 28, 2016
diff --git a/simpleBool.py b/simpleBool.py
@@ -0,0 +1,101 @@
+#
+# 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')
+