- Issue #6939: Fix file I/O objects in the `io` module to keep the original

  file position when calling `truncate()`.  It would previously change the
  file position to the given argument, which goes against the tradition of
  ftruncate() and other truncation APIs.  Patch by Pascal Chambon.

1 files changed, 11 insertions, 0 deletions

diff --git a/Lib/test/test_fileio.py b/Lib/test/test_fileio.py
index 91c5251d42..cdc3123718 100644
--- a/Lib/test/test_fileio.py
+++ b/Lib/test/test_fileio.py
@@ -329,6 +329,17 @@ class OtherFileTests(unittest.TestCase):
             f.close()
             self.fail("no error for invalid mode: %s" % bad_mode)
 
+    def testTruncate(self):
+        f = _FileIO(TESTFN, 'w')
+        f.write(bytes(bytearray(range(10))))
+        self.assertEqual(f.tell(), 10)
+        f.truncate(5)
+        self.assertEqual(f.tell(), 10)
+        self.assertEqual(f.seek(0, os.SEEK_END), 5)
+        f.truncate(15)
+        self.assertEqual(f.tell(), 5)
+        self.assertEqual(f.seek(0, os.SEEK_END), 15)
+
     def testTruncateOnWindows(self):
         def bug801631():
             # SF bug <http://www.python.org/sf/801631>