Merge pull request #1481 from weaversam8/bugfix/1476-symbol-eq

Fix `Symbol.__eq__` to return false when comparing with None

lark/grammar.py

@@ -16,7 +16,8 @@ def __init__(self, name: str) -> None:
         self.name = name
 
     def __eq__(self, other):
-        assert isinstance(other, Symbol), other
+        if not isinstance(other, Symbol):
+            return NotImplemented
         return self.is_term == other.is_term and self.name == other.name
 
     def __ne__(self, other):

tests/test_grammar.py

@@ -6,7 +6,7 @@
 from lark import Lark, Token, Tree, ParseError, UnexpectedInput
 from lark.load_grammar import GrammarError, GRAMMAR_ERRORS, find_grammar_errors, list_grammar_imports
 from lark.load_grammar import FromPackageLoader
-
+from lark.grammar import Symbol
 
 class TestGrammar(TestCase):
     def setUp(self):
@@ -296,8 +296,11 @@ def test_line_breaks(self):
         p.parse('ab')
 
 
+    def test_symbol_eq(self):
+        a = None
+        b = Symbol("abc")
 
-
+        self.assertNotEqual(a, b)
 
 
 if __name__ == '__main__':