Index: Modules/_fileio.c
===================================================================
--- Modules/_fileio.c	(révision 68774)
+++ Modules/_fileio.c	(copie de travail)
@@ -315,6 +315,9 @@
 			goto error;
 	}
 
+	if (append)
+		lseek(self->fd, 0, SEEK_END);
+
 	goto done;
 
  error:
Index: Lib/test/test_io.py
===================================================================
--- Lib/test/test_io.py	(révision 68774)
+++ Lib/test/test_io.py	(copie de travail)
@@ -233,6 +233,13 @@
             else:
                 self.fail("1/0 didn't raise an exception")
 
+    def test_with_open(self):
+        with open(support.TESTFN, "wb") as f:
+            f.write(b"xxx")
+        with open(support.TESTFN, "ab") as f:
+            # issue 5008: f.tell() returns 0 in append mode instead of 3
+            self.assertEqual(f.tell(), 3)
+
     def test_destructor(self):
         record = []
         class MyFileIO(io.FileIO):