sock.makefile().flush has UnboundLocalError bug

[Andrew Bennetts]

Binary package hint: python2.6

Sometimes calling .write/.writelines/.flush on an object returned from sock.makefile() gives a traceback ending with:

  File "/usr/lib/python2.6/socket.py", line 302, in flush
    del view, data # explicit free
UnboundLocalError: local variable 'view' referenced before assignment

This script demonstrates, but I've seen this with e.g. bzr's test suite too:

"""
import socket
import sys
import threading

sock_a, sock_b = socket.socketpair()
sock_a = socket.socket(_sock=sock_a)

def read_byte_then_close(s):
    data = s.recv(1)
    print >>sys.stderr, 'read:', repr(data)
    s.close()
    print >>sys.stderr, 'closed sock_b'
t = threading.Thread(target=read_byte_then_close, args=(sock_b,))
t.start()

file_a = sock_a.makefile('w')
file_a.writelines(['a'*8192]*1000)
file_a.flush()
t.join()
"""

(It might not be a strictly minimal reproduction, but it's not too far off.)

The cause of the bug is pretty trivially obvious on inspection: the 'view' variable is indeed never defined in that method. Running pyflakes on socket.py finds that bug on line 302, and also a similar one on line 399 in the read() method.

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: python2.6 2.6.6~rc1-1ubuntu1
ProcVersionSignature: Ubuntu 2.6.35-14.19-generic 2.6.35
Uname: Linux 2.6.35-14-generic i686
Architecture: i386
Date: Mon Aug 9 16:55:04 2010
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release i386 (20100429)
ProcEnviron:
 LANG=en_AU.utf8
 SHELL=/bin/bash
SourcePackage: python2.6

[Martin Packman (gz)]

This is from a bad merge:
http://svn.python.org/view?view=rev&revision=83624

The original diff:
http://svn.python.org/view/python/trunk/Lib/socket.py?r1=75412&r2=75411&pathrev=75412

The merged diff:
http://svn.python.org/view/python/branches/release26-maint/Lib/socket.py?r1=81488&r2=83624

Kept the addition of 'view' even though that part of the change wasn't taken.

[Andrew Bennetts (spiv)]

(On closer inspection the second pyflakes report about 'del data' in _fileobject.read() is spurious.)

[Launchpad Janitor (janitor)]

This bug was fixed in the package python2.6 - 2.6.6~rc2-1ubuntu1

---------------
python2.6 (2.6.6~rc2-1ubuntu1) maverick; urgency=low

  * Merge with Debian; remaining changes:
    - Regenerate the control file.

python2.6 (2.6.6~rc2-1) unstable; urgency=low

  * Python 2.6.6 release candidate 2.
    - Fix issue #8688: Revert regression introduced in 2.6.6rc1 (making
      Distutils recalculate MANIFEST every time).
    - Fix issue #9543: Fix regression in socket.py introduced in
      Python 2.6.6 rc1 in r83624. LP: #615240.
    - Fix issue #7567: Don't call `setupterm' twice.
  * Update README for python2.6-minimal. Closes: #593391.
 -- Matthias Klose <email address hidden> Wed, 18 Aug 2010 10:01:24 +0200