From: Raymond Hettinger <python@rcn.com>
Date: Mon, 12 Sep 2016 05:02:28 +0000 (-0700)
Subject: Issue #28071: Add early-out for differencing from an empty set.
X-Git-Tag: v3.6.0b1~17^2~4
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=4103e4dfbce8b6d9579565ab64868a721b01d2a1;p=thirdparty%2FPython%2Fcpython.git

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

diff --git a/Misc/NEWS b/Misc/NEWS
index 1c253b6366e0..083b33f7dd5e 100644
--- a/Misc/NEWS
+++ b/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)
 
diff --git a/Objects/setobject.c b/Objects/setobject.c
index 6dd403f30fa3..5846045376d6 100644
--- a/Objects/setobject.c
+++ b/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);
     }