Issue #28071: Add early-out for differencing from an empty set.

Author: rhettinger

Misc/NEWS

@@ -33,6 +33,8 @@ Core and Builtins
 
 - Issue #28046: Remove platform-specific directories from sys.path.
 
+- Issue #28071: Add early-out for differencing from an empty set.
+
 - Issue #25758: Prevents zipimport from unnecessarily encoding a filename
  (patch by Eryk Sun)
 

Objects/setobject.c

@@ -1476,6 +1476,10 @@ PyDoc_STRVAR(isdisjoint_doc,
 static int
 set_difference_update_internal(PySetObject *so, PyObject *other)
 {
+ if (PySet_GET_SIZE(so) == 0) {
+ return 0;
+ }
+
  if ((PyObject *)so == other)
  return set_clear_internal(so);
 
@@ -1550,6 +1554,10 @@ set_difference(PySetObject *so, PyObject *other)
  Py_ssize_t pos = 0;
  int rv;
 
+ if (PySet_GET_SIZE(so) == 0) {
+ return set_copy(so);
+ }
+
  if (!PyAnySet_Check(other) && !PyDict_CheckExact(other)) {
  return set_copy_and_difference(so, other);
  }