py/objset: Check that RHS of a binary op is a set/frozenset.

CPython docs explicitly state that the RHS of a set/frozenset binary op
must be a set to prevent user errors.  It also preserves commutativity of
the ops, eg: "abc" & set() is a TypeError, and so should be set() & "abc".

This change actually decreases unix (x64) code by 160 bytes; it increases
stm32 by 4 bytes and esp8266 by 28 bytes (but previous patch already
introduced a much large saving).

py/objset.c

@@ -463,6 +463,10 @@ STATIC mp_obj_t set_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
     #else
     bool update = true;
     #endif
+    if (op != MP_BINARY_OP_IN && !is_set_or_frozenset(rhs)) {
+        // For all ops except containment the RHS must be a set/frozenset
+        return MP_OBJ_NULL;
+    }
     switch (op) {
         case MP_BINARY_OP_OR:
             return set_union(lhs, rhs);

tests/basics/set_binop.py

@@ -47,6 +47,18 @@ s1 = s2 = set('abc')
 s1 -= set('ad')
 print(s1 is s2, len(s1))
 
+# RHS must be a set
+try:
+    print(set('12') >= '1')
+except TypeError:
+    print('TypeError')
+
+# RHS must be a set
+try:
+    print(set('12') <= '123')
+except TypeError:
+    print('TypeError')
+
 # unsupported operator
 try:
     set('abc') * 2

tests/misc/non_compliant.py

@@ -39,18 +39,6 @@ try:
 except NotImplementedError:
     print('NotImplementedError')
 
-# should raise type error
-try:
-    print(set('12') >= '1')
-except TypeError:
-    print('TypeError')
-
-# should raise type error
-try:
-    print(set('12') <= '123')
-except TypeError:
-    print('TypeError')
-
 # uPy raises TypeError, shold be ValueError
 try:
     '%c' % b'\x01\x02'

tests/misc/non_compliant.py.exp

@@ -3,8 +3,6 @@ AttributeError
 TypeError
 NotImplementedError
 NotImplementedError
-True
-True
 TypeError, ValueError
 NotImplementedError
 NotImplementedError