diff --git a/hgdemandimport/py3tokenize.py b/hgdemandimport/py3tokenize.py
--- a/hgdemandimport/py3tokenize.py
+++ b/hgdemandimport/py3tokenize.py
@@ -62,6 +62,7 @@
 # * Adjusted for relative imports.
 # * absolute_import added.
 # * Removed re.ASCII.
+# * Various backports to work on Python 2.7.
 
 from __future__ import absolute_import
 
@@ -256,7 +257,7 @@
 class StopTokenizing(Exception): pass
 
 
-class Untokenizer:
+class Untokenizer(object):
 
     def __init__(self):
         self.tokens = []
@@ -503,11 +504,22 @@
     """
     # This import is here to avoid problems when the itertools module is not
     # built yet and tokenize is imported.
-    from itertools import chain, repeat
+    from itertools import repeat
     encoding, consumed = detect_encoding(readline)
-    rl_gen = iter(readline, b"")
-    empty = repeat(b"")
-    return _tokenize(chain(consumed, rl_gen, empty).__next__, encoding)
+
+    def lines():
+        for line in consumed:
+            yield line
+
+        while True:
+            try:
+                yield readline()
+            except StopIteration:
+                break
+
+        yield repeat(b'')
+
+    return _tokenize(lines(), encoding)
 
 
 def _tokenize(readline, encoding):
@@ -531,7 +543,7 @@
             # hence `line` itself will always be overwritten at the end
             # of this loop.
             last_line = line
-            line = readline()
+            line = next(readline)
         except StopIteration:
             line = b''