call PyErr_Clear() when ignoring error from PyNumber_Int (closes #15516)

Patch from Tom Tromey.

Lib/test/test_format.py

@@ -234,6 +234,16 @@ class FormatTest(unittest.TestCase):
         testformat('%g', 1.1, '1.1')
         testformat('%#g', 1.1, '1.10000')
 
+        # Regression test for http://bugs.python.org/issue15516.
+        class IntFails(object):
+            def __int__(self):
+                raise TestFailed
+            def __long__(self):
+                return 0
+
+        fst = IntFails()
+        testformat("%x", fst, '0')
+
         # Test exception for unknown format characters
         if verbose:
             print 'Testing exceptions'

Misc/NEWS

@@ -9,6 +9,9 @@ What's New in Python 2.7.4
 Core and Builtins
 -----------------
 
+- Issue #15516: Fix a bug in PyString_FromFormat where it failed to properly
+  ignore errors from a __int__() method.
+
 - Issue #16839: Fix a segfault when calling unicode() on a classic class early
   in interpreter initialization.
 

Objects/stringobject.c

@@ -4489,7 +4489,10 @@ PyString_Format(PyObject *format, PyObject *args)
                     }
                     else {
                         iobj = PyNumber_Int(v);
-                        if (iobj==NULL) iobj = PyNumber_Long(v);
+                        if (iobj==NULL) {
+			    PyErr_Clear();
+			    iobj = PyNumber_Long(v);
+			}
                     }
                     if (iobj!=NULL) {
                         if (PyInt_Check(iobj)) {