Fixed partials (Issue #398)

lark/utils.py

@@ -160,7 +160,7 @@ def smart_decorator(f, create_decorator):
 
     elif isinstance(f, partial):
         # wraps does not work for partials in 2.7: https://bugs.python.org/issue3445
-        return create_decorator(f.__func__, True)
+        return wraps(f.func)(create_decorator(f.func, True))
 
     else:
         return create_decorator(f.__func__.__call__, True)

tests/test_trees.py

@@ -4,6 +4,7 @@ import unittest
 from unittest import TestCase
 import copy
 import pickle
+import functools
 
 from lark.tree import Tree
 from lark.visitors import Transformer, Interpreter, visit_children_decor, v_args, Discard
@@ -146,6 +147,22 @@ class TestTrees(TestCase):
         res = T().transform(t)
         self.assertEqual(res, 2.9)
 
+    def test_partial(self):
+
+        tree = Tree("start", [Tree("a", ["test1"]), Tree("b", ["test2"])])
+
+        def test(t, s):
+            return s.upper()
+
+        @v_args(inline=True)
+        class T(Transformer):
+            a = functools.partial(test)
+            b = functools.partial(lambda t, s: s + "!")
+
+        res = T().transform(tree)
+        assert res.children == ["TEST1", "test2!"]
+
+
     def test_discard(self):
         class MyTransformer(Transformer):
             def a(self, args):