Bind dispatched methods, and don't rely on "self" argument to infer methods

multipledispatch/core.py

@@ -57,7 +57,7 @@ def dispatch(*types, **kwargs):
     def _(func):
         name = func.__name__
 
-        if ismethod(func):
+        if ismethod(func) and isinclass():
             dispatcher = inspect.currentframe().f_back.f_locals.get(name,
                 MethodDispatcher(name))
         else:
@@ -78,3 +78,11 @@ def ismethod(func):
     """
     spec = inspect.getargspec(func)
     return spec and spec.args and spec.args[0] == 'self'
+
+
+def isinclass(n=1):
+    """ Is the nth previous frame in a class definition?"""
+    frame = inspect.currentframe().f_back  # escape from current function
+    for _ in range(n):
+        frame = getattr(frame, 'f_back')
+    return '__module__' in frame.f_locals

multipledispatch/dispatcher.py

@@ -203,14 +203,16 @@ class MethodDispatcher(Dispatcher):
         Dispatcher
     """
     def __get__(self, instance, owner):
-        self.obj = instance
-        self.cls = owner
-        return self
+        dispatcher = self
+        def method(self, *args, **kwargs):
+            return dispatcher(self, *args, **kwargs)
+        method.__name__ = self.name
+        return method.__get__(instance, owner)
 
-    def __call__(self, *args, **kwargs):
+    def __call__(self, obj, *args, **kwargs):
         types = tuple([type(arg) for arg in args])
         func = self.resolve(types)
-        return func(self.obj, *args, **kwargs)
+        return func(obj, *args, **kwargs)
 
 
 def str_signature(sig):

multipledispatch/tests/test_core.py

@@ -189,6 +189,21 @@ def g(self, x):
 
 
 def test_methods_multiple_dispatch():
+    class Foo(object):
+        @dispatch(A)
+        def f(self, y):
+            return 1
+
+        @dispatch(C)
+        def f(self, y):
+            return 2
+
+    foo = Foo()
+    assert foo.f(A()) == 1
+    assert foo.f(C()) == 2
+
+
+def test_methods_multiple_dispatch_fail():
     class Foo(object):
         @dispatch(A, A)
         def f(x, y):
@@ -198,8 +213,63 @@ def f(x, y):
         def f(x, y):
             return 2
 
+        @dispatch(int)
+        def f(x, y):  # 'x' as self
+            return 1 + y
 
     foo = Foo()
+    # We require the 'self' argument to be used to infer methods
     assert foo.f(A(), A()) == 1
     assert foo.f(A(), C()) == 2
     assert foo.f(C(), C()) == 2
+    assert raises(TypeError, lambda: foo.f(2))
+
+
+def test_function_with_self():
+    @dispatch(A, A)
+    def f(self, x):
+        return 1
+
+    @dispatch(A, C)
+    def f(self, x):
+        return 2
+
+    @dispatch(C, A)
+    def f(self, x):
+        return 3
+
+    @dispatch(C, C)
+    def f(self, x):
+        return 4
+
+    assert f(A(), A()) == 1
+    assert f(A(), C()) == 2
+    assert f(C(), A()) == 3
+    assert f(C(), C()) == 4
+
+
+def test_method_dispatch_is_safe():
+    class Foo(object):
+        def __init__(self, x):
+            self.x = x
+
+        @dispatch(int)
+        def f(self, y):
+            return self.x + y
+
+        @dispatch(float)
+        def f(self, y):
+            return self.x - y
+
+    foo1 = Foo(1)
+    foo2 = Foo(2)
+    assert foo1.f(1) == 2
+    assert foo1.f(1.0) == 0.0
+    assert foo2.f(1) == 3
+    assert foo2.f(1.0) == 1.0
+    f1 = foo1.f
+    f2 = foo2.f
+    assert f1(1) == 2
+    assert f1(1.0) == 0.0
+    assert f2(1) == 3
+    assert f2(1.0) == 1.0