I'm trying to use a tar stream to a Python tarfile object but each time I do have a  TypeError: can't concat bytes to str error

Here is my test:
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#!/usr/bin/python3.4

import tarfile
import sys

tarobj = tarfile.open(mode='r|', fileobj=sys.stdin)
print(tarobj)
tarobj.close()
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$ tar cvf test.tar.gz tests/
tests/
tests/foo1
tests/foo/
tests/foo/bar
$ tar -O -xvf test.tar | ./tarstream.py
tests/
tests/foo1
tests/foo/
tests/foo/bar
Traceback (most recent call last):
  File "./tarstream.py", line 6, in <module>
    tarobj = tarfile.open(mode='r|', fileobj=sys.stdin)
  File "/usr/lib/python3.4/tarfile.py", line 1578, in open
    t = cls(name, filemode, stream, **kwargs)
  File "/usr/lib/python3.4/tarfile.py", line 1470, in __init__
    self.firstmember = self.next()
  File "/usr/lib/python3.4/tarfile.py", line 2249, in next
    tarinfo = self.tarinfo.fromtarfile(self)
  File "/usr/lib/python3.4/tarfile.py", line 1082, in fromtarfile
    buf = tarfile.fileobj.read(BLOCKSIZE)
  File "/usr/lib/python3.4/tarfile.py", line 535, in read
    buf = self._read(size)
  File "/usr/lib/python3.4/tarfile.py", line 543, in _read
    return self.__read(size)
  File "/usr/lib/python3.4/tarfile.py", line 569, in __read
    self.buf += buf
TypeError: can't concat bytes to str

Regards,
Carl Chenet