Only the parts which are relevant for 3.x branch.

Merged revisions 78757-78758,78769,78815 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk

........
  r78757 | florent.xicluna | 2010-03-07 13:14:25 +0100 (dim, 07 mar 2010) | 2 lines

  Fix some py3k warnings in the standard library.
........
  r78758 | florent.xicluna | 2010-03-07 13:18:33 +0100 (dim, 07 mar 2010) | 4 lines

  Issue #7849: Now the utility ``check_warnings`` verifies if the warnings are
  effectively raised.  A new utility ``check_py3k_warnings`` deals with py3k warnings.
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  r78769 | florent.xicluna | 2010-03-07 20:14:12 +0100 (dim, 07 mar 2010) | 2 lines

  Refresh the documentation for the test.test_support module.
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  r78815 | florent.xicluna | 2010-03-09 20:57:01 +0100 (mar, 09 mar 2010) | 2 lines

  #7772: Fix test_py3kwarn. Now the test suite could pass with "-3" flag.
........

Lib/_pyio.py

@@ -828,7 +828,7 @@ class BytesIO(BufferedIOBase):
         if self.closed:
             raise ValueError("seek on closed file")
         try:
-            pos = pos.__index__()
+            pos.__index__
         except AttributeError as err:
             raise TypeError("an integer is required") from err
         if whence == 0:
@@ -853,8 +853,13 @@ class BytesIO(BufferedIOBase):
             raise ValueError("truncate on closed file")
         if pos is None:
             pos = self._pos
-        elif pos < 0:
-            raise ValueError("negative truncate position %r" % (pos,))
+        else:
+            try:
+                pos.__index__
+            except AttributeError as err:
+                raise TypeError("an integer is required") from err
+            if pos < 0:
+                raise ValueError("negative truncate position %r" % (pos,))
         del self._buffer[pos:]
         return pos
 
@@ -1803,6 +1808,10 @@ class TextIOWrapper(TextIOBase):
         if n is None:
             n = -1
         decoder = self._decoder or self._get_decoder()
+        try:
+            n.__index__
+        except AttributeError as err:
+            raise TypeError("an integer is required") from err
         if n < 0:
             # Read everything.
             result = (self._get_decoded_chars() +