py: Be more restrictive binding self when looking up instance attrs.

When looking up and extracting an attribute of an instance, some
attributes must bind self as the first argument to make a working method
call.  Previously to this patch, any attribute that was callable had self
bound as the first argument.  But Python specs require the check to be
more restrictive, and only functions, closures and generators should have
self bound as the first argument

Addresses issue #1675.

py/runtime.c

@@ -947,7 +947,11 @@ void mp_convert_member_lookup(mp_obj_t self, const mp_obj_type_t *type, mp_obj_t
     } else if (MP_OBJ_IS_TYPE(member, &mp_type_type)) {
         // Don't try to bind types (even though they're callable)
         dest[0] = member;
-    } else if (mp_obj_is_callable(member)) {
+    } else if (MP_OBJ_IS_FUN(member)
+        || (MP_OBJ_IS_OBJ(member)
+            && (((mp_obj_base_t*)MP_OBJ_TO_PTR(member))->type->name == MP_QSTR_closure
+                || ((mp_obj_base_t*)MP_OBJ_TO_PTR(member))->type->name == MP_QSTR_generator))) {
+        // only functions, closures and generators objects can be bound to self
         #if MICROPY_BUILTIN_METHOD_CHECK_SELF_ARG
         if (self == MP_OBJ_NULL && mp_obj_get_type(member) == &mp_type_fun_builtin) {
             // we extracted a builtin method without a first argument, so we must

tests/basics/class_bind_self.py

@@ -0,0 +1,54 @@
+# test for correct binding of self when accessing attr of an instance
+
+class A:
+    def __init__(self, arg):
+        self.val = arg
+    def __str__(self):
+        return 'A.__str__ ' + str(self.val)
+    def __call__(self, arg):
+        return 'A.__call__', arg
+    def foo(self, arg):
+        return 'A.foo', self.val, arg
+
+def make_closure(x_in):
+    x = x_in
+    def closure(y):
+        return x, y is c
+    return closure
+
+class C:
+    # these act like methods and bind self
+
+    def f1(self, arg):
+        return 'C.f1', self is c, arg
+    f2 = lambda self, arg: ('C.f2', self is c, arg)
+    f3 = make_closure('f3') # closure
+    def f4(self, arg): # generator
+        yield self is c, arg
+
+    # these act like simple variables and don't bind self
+
+    f5 = int # builtin type
+    f6 = abs # builtin function
+    f7 = A # user type
+    f8 = A(8) # user instance which is callable
+    f9 = A(9).foo # user bound method
+
+c = C()
+print(c.f1(1))
+print(c.f2(2))
+print(c.f3())
+print(next(c.f4(4)))
+print(c.f5(5))
+#print(c.f6(-6)) not working in uPy
+print(c.f7(7))
+print(c.f8(8))
+print(c.f9(9))
+
+# not working in uPy
+#class C(list):
+#    # this acts like a method and binds self
+#    f1 = list.extend
+#c = C()
+#c.f1([3, 1, 2])
+#print(c)