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import re
class BooleanExpression:
# A simple evaluator of boolean expressions.
#
# Grammar:
# expr :: or_expr
# or_expr :: and_expr ('||' and_expr)*
# and_expr :: not_expr ('&&' not_expr)*
# not_expr :: '!' not_expr
# '(' or_expr ')'
# identifier
# identifier :: [-+=._a-zA-Z0-9]+
# Evaluates `string` as a boolean expression.
# Returns True or False. Throws a ValueError on syntax error.
#
# Variables in `variables` are true.
# Substrings of `triple` are true.
# 'true' is true.
# All other identifiers are false.
@staticmethod
def evaluate(string, variables, triple=""):
try:
parser = BooleanExpression(string, set(variables), triple)
return parser.parseAll()
except ValueError as e:
raise ValueError(str(e) + ('\nin expression: %r' % string))
#####
def __init__(self, string, variables, triple=""):
self.tokens = BooleanExpression.tokenize(string)
self.variables = variables
self.variables.add('true')
self.triple = triple
self.value = None
self.token = None
# Singleton end-of-expression marker.
END = object()
# Tokenization pattern.
Pattern = re.compile(r'\A\s*([()]|[-+=._a-zA-Z0-9]+|&&|\|\||!)\s*(.*)\Z')
@staticmethod
def tokenize(string):
while True:
m = re.match(BooleanExpression.Pattern, string)
if m is None:
if string == "":
yield BooleanExpression.END;
return
else:
raise ValueError("couldn't parse text: %r" % string)
token = m.group(1)
string = m.group(2)
yield token
def quote(self, token):
if token is BooleanExpression.END:
return '<end of expression>'
else:
return repr(token)
def accept(self, t):
if self.token == t:
self.token = next(self.tokens)
return True
else:
return False
def expect(self, t):
if self.token == t:
if self.token != BooleanExpression.END:
self.token = next(self.tokens)
else:
raise ValueError("expected: %s\nhave: %s" %
(self.quote(t), self.quote(self.token)))
def isIdentifier(self, t):
if (t is BooleanExpression.END or t == '&&' or t == '||' or
t == '!' or t == '(' or t == ')'):
return False
return True
def parseNOT(self):
if self.accept('!'):
self.parseNOT()
self.value = not self.value
elif self.accept('('):
self.parseOR()
self.expect(')')
elif not self.isIdentifier(self.token):
raise ValueError("expected: '!' or '(' or identifier\nhave: %s" %
self.quote(self.token))
else:
self.value = (self.token in self.variables or
self.token in self.triple)
self.token = next(self.tokens)
def parseAND(self):
self.parseNOT()
while self.accept('&&'):
left = self.value
self.parseNOT()
right = self.value
# this is technically the wrong associativity, but it
# doesn't matter for this limited expression grammar
self.value = left and right
def parseOR(self):
self.parseAND()
while self.accept('||'):
left = self.value
self.parseAND()
right = self.value
# this is technically the wrong associativity, but it
# doesn't matter for this limited expression grammar
self.value = left or right
def parseAll(self):
self.token = next(self.tokens)
self.parseOR()
self.expect(BooleanExpression.END)
return self.value
#######
# Tests
import unittest
class TestBooleanExpression(unittest.TestCase):
def test_variables(self):
variables = {'its-true', 'false-lol-true', 'under_score',
'e=quals', 'd1g1ts'}
self.assertTrue(BooleanExpression.evaluate('true', variables))
self.assertTrue(BooleanExpression.evaluate('its-true', variables))
self.assertTrue(BooleanExpression.evaluate('false-lol-true', variables))
self.assertTrue(BooleanExpression.evaluate('under_score', variables))
self.assertTrue(BooleanExpression.evaluate('e=quals', variables))
self.assertTrue(BooleanExpression.evaluate('d1g1ts', variables))
self.assertFalse(BooleanExpression.evaluate('false', variables))
self.assertFalse(BooleanExpression.evaluate('True', variables))
self.assertFalse(BooleanExpression.evaluate('true-ish', variables))
self.assertFalse(BooleanExpression.evaluate('not_true', variables))
self.assertFalse(BooleanExpression.evaluate('tru', variables))
def test_triple(self):
triple = 'arch-vendor-os'
self.assertTrue(BooleanExpression.evaluate('arch-', {}, triple))
self.assertTrue(BooleanExpression.evaluate('ar', {}, triple))
self.assertTrue(BooleanExpression.evaluate('ch-vend', {}, triple))
self.assertTrue(BooleanExpression.evaluate('-vendor-', {}, triple))
self.assertTrue(BooleanExpression.evaluate('-os', {}, triple))
self.assertFalse(BooleanExpression.evaluate('arch-os', {}, triple))
def test_operators(self):
self.assertTrue(BooleanExpression.evaluate('true || true', {}))
self.assertTrue(BooleanExpression.evaluate('true || false', {}))
self.assertTrue(BooleanExpression.evaluate('false || true', {}))
self.assertFalse(BooleanExpression.evaluate('false || false', {}))
self.assertTrue(BooleanExpression.evaluate('true && true', {}))
self.assertFalse(BooleanExpression.evaluate('true && false', {}))
self.assertFalse(BooleanExpression.evaluate('false && true', {}))
self.assertFalse(BooleanExpression.evaluate('false && false', {}))
self.assertFalse(BooleanExpression.evaluate('!true', {}))
self.assertTrue(BooleanExpression.evaluate('!false', {}))
self.assertTrue(BooleanExpression.evaluate(' ((!((false) )) ) ', {}))
self.assertTrue(BooleanExpression.evaluate('true && (true && (true))', {}))
self.assertTrue(BooleanExpression.evaluate('!false && !false && !! !false', {}))
self.assertTrue(BooleanExpression.evaluate('false && false || true', {}))
self.assertTrue(BooleanExpression.evaluate('(false && false) || true', {}))
self.assertFalse(BooleanExpression.evaluate('false && (false || true)', {}))
# Evaluate boolean expression `expr`.
# Fail if it does not throw a ValueError containing the text `error`.
def checkException(self, expr, error):
try:
BooleanExpression.evaluate(expr, {})
self.fail("expression %r didn't cause an exception" % expr)
except ValueError as e:
if -1 == str(e).find(error):
self.fail(("expression %r caused the wrong ValueError\n" +
"actual error was:\n%s\n" +
"expected error was:\n%s\n") % (expr, e, error))
except BaseException as e:
self.fail(("expression %r caused the wrong exception; actual " +
"exception was: \n%r") % (expr, e))
def test_errors(self):
self.checkException("ba#d",
"couldn't parse text: '#d'\n" +
"in expression: 'ba#d'")
self.checkException("true and true",
"expected: <end of expression>\n" +
"have: 'and'\n" +
"in expression: 'true and true'")
self.checkException("|| true",
"expected: '!' or '(' or identifier\n" +
"have: '||'\n" +
"in expression: '|| true'")
self.checkException("true &&",
"expected: '!' or '(' or identifier\n" +
"have: <end of expression>\n" +
"in expression: 'true &&'")
self.checkException("",
"expected: '!' or '(' or identifier\n" +
"have: <end of expression>\n" +
"in expression: ''")
self.checkException("*",
"couldn't parse text: '*'\n" +
"in expression: '*'")
self.checkException("no wait stop",
"expected: <end of expression>\n" +
"have: 'wait'\n" +
"in expression: 'no wait stop'")
self.checkException("no-$-please",
"couldn't parse text: '$-please'\n" +
"in expression: 'no-$-please'")
self.checkException("(((true && true) || true)",
"expected: ')'\n" +
"have: <end of expression>\n" +
"in expression: '(((true && true) || true)'")
self.checkException("true (true)",
"expected: <end of expression>\n" +
"have: '('\n" +
"in expression: 'true (true)'")
self.checkException("( )",
"expected: '!' or '(' or identifier\n" +
"have: ')'\n" +
"in expression: '( )'")
if __name__ == '__main__':
unittest.main()
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