gh-104018: disallow "z" format specifier in %-format of byte strings (GH-104033)

belm0 · blurb-it[bot] · web-flow · commit 3ed8c882902a · 2023-05-01T20:47:14.000+01:00
PEP-0682 specified that %-formatting would not support the "z" specifier, but it was unintentionally allowed for bytes. This PR makes use of the "z" flag an error for %-formatting in a bytestring. Issue: #104018 --------- Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
diff --git a/Lib/test/test_format.py b/Lib/test/test_format.py
@@ -619,6 +619,8 @@ def test_specifier_z_error(self):
         error_msg = re.escape("unsupported format character 'z'")
         with self.assertRaisesRegex(ValueError, error_msg):
             "%z.1f" % 0  # not allowed in old style string interpolation
+        with self.assertRaisesRegex(ValueError, error_msg):
+            b"%z.1f" % 0
 
 
 if __name__ == "__main__":
diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-05-01-12-03-52.gh-issue-104018.PFxGS4.rst b/Misc/NEWS.d/next/Core and Builtins/2023-05-01-12-03-52.gh-issue-104018.PFxGS4.rst
@@ -0,0 +1 @@
+Disallow the "z" format specifier in %-format of bytes objects.
diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
@@ -705,7 +705,6 @@ _PyBytes_FormatEx(const char *format, Py_ssize_t format_len,
                 case ' ': flags |= F_BLANK; continue;
                 case '#': flags |= F_ALT; continue;
                 case '0': flags |= F_ZERO; continue;
-                case 'z': flags |= F_NO_NEG_0; continue;
                 }
                 break;
             }
