Re-allow cursing dunder methods with non-functions. (clarete#35)

Closes: clarete#34, clarete#20

forbiddenfruit/__init__.py

@@ -328,7 +328,7 @@ def _curse_special(klass, attr, func):
     Curse one of the "dunder" methods, i.e. methods beginning with __ which have a
     precial resolution code path
     """
-    assert isinstance(func, FunctionType)
+    assert callable(func)
 
     @wraps(func)
     def wrapper(*args, **kwargs):

tests/unit/test_forbidden_fruit.py

@@ -16,7 +16,7 @@ def almost_equal(a, b, e=0.001):
 
 skip_legacy = nottest if sys.version_info < (3, 3) else istest
 
-def test_cursing_a_builting_class():
+def test_cursing_a_builtin_class():
 
     # Given that I have a function that returns *blah*
     def words_of_wisdom(self):
@@ -30,7 +30,7 @@ def words_of_wisdom(self):
     assert 'words_of_wisdom' in dir(int)
 
 
-def test_cursing_a_builting_class_with_a_class_method():
+def test_cursing_a_builtin_class_with_a_class_method():
 
     # Given that I have a function that returns *blah*
     def hello(self):
@@ -44,6 +44,20 @@ def hello(self):
     assert 'hello' in dir(str)
 
 
+@skip_legacy
+def test_cursing_a_builtin_class_dunder_with_a_random_callable():
+    # Given that I have an object that returns *blah*
+    class Twelver(object):
+        def __call__(self, one, two):
+            return 12
+
+    # When I try to curse a built-in class's __sub__ with that function
+    curse(str, "__sub__", Twelver())
+
+    # Then I see that the class was cursed
+    assert ("hello" - "world") == 12
+
+
 def test_reversing_a_builtin():
     # Given that I have a cursed object
     curse(str, 'stuff', property(lambda s: s * 2))

tox.ini

@@ -7,6 +7,7 @@
 envlist = py27, py30, py33, py34, py35, py36, py37
 
 [testenv]
+whitelist_externals = make
 commands = make
 deps =
     nose