py: Implement fallback for equality check for all types.

Return "not equal" for objects that don't implement equality check.
This is as per Python specs.

py/obj.c

@@ -190,12 +190,19 @@ mp_int_t mp_obj_hash(mp_obj_t o_in) {
     }
 }
 
-// this function implements the '==' operator (and so the inverse of '!=')
+// This function implements the '==' operator (and so the inverse of '!=').
-// from the python language reference:
+//
+// From the Python language reference:
+// (https://docs.python.org/3/reference/expressions.html#not-in)
 // "The objects need not have the same type. If both are numbers, they are converted
 // to a common type. Otherwise, the == and != operators always consider objects of
 // different types to be unequal."
-// note also that False==0 and True==1 are true expressions
+//
+// This means that False==0 and True==1 are true expressions.
+//
+// Furthermore, from the v3.4.2 code for object.c: "Practical amendments: If rich
+// comparison returns NotImplemented, == and != are decided by comparing the object
+// pointer."
 bool mp_obj_equal(mp_obj_t o1, mp_obj_t o2) {
     if (o1 == o2) {
         return true;
@@ -239,14 +246,9 @@ bool mp_obj_equal(mp_obj_t o1, mp_obj_t o2) {
         }
     }
 
-    if (MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_TERSE) {
+    // equality not implemented, and objects are not the same object, so
-        nlr_raise(mp_obj_new_exception_msg(&mp_type_NotImplementedError,
+    // they are defined as not equal
-            "equality for given types not yet implemented"));
+    return false;
-    } else {
-        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_NotImplementedError,
-            "equality for '%s' and '%s' types not yet implemented",
-            mp_obj_get_type_str(o1), mp_obj_get_type_str(o2)));
-    }
 }
 
 mp_int_t mp_obj_get_int(mp_const_obj_t arg) {

tests/basics/equal_class.py

@@ -0,0 +1,25 @@
+# test equality for classes/instances to other types
+
+class A:
+    pass
+
+class B:
+    pass
+
+class C(A):
+    pass
+
+print(A == None)
+print(None == A)
+
+print(A == A)
+print(A() == A)
+print(A() == A())
+
+print(A == B)
+print(A() == B)
+print(A() == B())
+
+print(A == C)
+print(A() == C)
+print(A() == C())