diff -r 4fb829f8c04d Lib/tempfile.py
--- a/Lib/tempfile.py	Wed Mar 18 11:29:47 2015 +0100
+++ b/Lib/tempfile.py	Thu Mar 19 13:18:44 2015 +0100
@@ -426,7 +426,9 @@
 
     # iter() doesn't use __getattr__ to find the __iter__ method
     def __iter__(self):
-        return iter(self.file)
+        # don't return iter(self.file), but yield from it to avoid closing
+        # file as long as it's being used as iterator, see issue #23000
+        yield from iter(self.file)
 
 
 def NamedTemporaryFile(mode='w+b', buffering=-1, encoding=None,
diff -r 4fb829f8c04d Lib/test/test_tempfile.py
--- a/Lib/test/test_tempfile.py	Wed Mar 18 11:29:47 2015 +0100
+++ b/Lib/test/test_tempfile.py	Thu Mar 19 13:18:44 2015 +0100
@@ -707,6 +707,18 @@
             # No reference cycle was created.
             self.assertIsNone(wr())
 
+    def test_iter(self):
+        # getting iterator from a temporary file should keep it alive
+        # as long as it's being iterated over
+        lines = [b'spam\n', b'eggs\n', b'beans\n']
+        def make_file():
+            f = tempfile.NamedTemporaryFile(mode='w+b')
+            f.write(b''.join(lines))
+            f.seek(0)
+            return iter(f)
+        for i, l in enumerate(make_file()):
+            self.assertEqual(l, lines[i])
+
     def test_creates_named(self):
         # NamedTemporaryFile creates files with names
         f = tempfile.NamedTemporaryFile()