Issue #16601: Restarting iteration over tarfile no more continues from where

it left off.  Patch by Michael Birtwell.

Lib/tarfile.py

@@ -2462,15 +2462,17 @@ class TarIter:
         # Fix for SF #1100429: Under rare circumstances it can
         # happen that getmembers() is called during iteration,
         # which will cause TarIter to stop prematurely.
-        if not self.tarfile._loaded:
+
+        if self.index == 0 and self.tarfile.firstmember is not None:
+            tarinfo = self.tarfile.next()
+        elif self.index < len(self.tarfile.members):
+            tarinfo = self.tarfile.members[self.index]
+        elif not self.tarfile._loaded:
             tarinfo = self.tarfile.next()
             if not tarinfo:
                 self.tarfile._loaded = True
                 raise StopIteration
         else:
-            try:
-                tarinfo = self.tarfile.members[self.index]
-            except IndexError:
             raise StopIteration
         self.index += 1
         return tarinfo

Lib/test/test_tarfile.py

@@ -345,6 +345,14 @@ class MiscReadTest(CommonReadTest):
         finally:
             os.remove(empty)
 
+    def test_parallel_iteration(self):
+        # Issue #16601: Restarting iteration over tarfile continued
+        # from where it left off.
+        with tarfile.open(self.tarname) as tar:
+            for m1, m2 in zip(tar, tar):
+                self.assertEqual(m1.offset, m2.offset)
+                self.assertEqual(m1.name, m2.name)
+
 
 class StreamReadTest(CommonReadTest):
 

Misc/ACKS

@@ -96,6 +96,7 @@ Natalia B. Bidart
 David Binger
 Dominic Binks
 Philippe Biondi
+Michael Birtwell
 Stuart Bishop
 Roy Bixler
 Jonathan Black

Misc/NEWS

@@ -26,6 +26,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #16601: Restarting iteration over tarfile no more continues from where
+  it left off.  Patch by Michael Birtwell.
+
 - Issue 16584: in filecomp._cmp, catch IOError as well as os.error.
   Patch by Till Maas.