Only relevant to posix.
asyncore.file_dispatcher closes the file descriptor
behind the file object, and not the file object itself.
When another file gets opened, it gets the next
available fd, which on posix, is the one just released
by the close.

Tested on python 2.2.3 on RedHat Enterprise Linux 3 and
python 2.2.1 on HP Tru64 unix. See attached script for
details and a solution. 'case 1' should show the
problem regardless of the garbage collection strategy
in python. 'case 2' relies on the file object being
closed as soon as the last reference to it disappears,
which seems to be the (current?) behaviour.

[djh900@dh djh900]$ python file_dispatcher_bug.py
case 1:
 (Read 'I am the first pipe\n' from pipe)
 (pipe closing. fd== 3 )
 (Read '' from pipe)
firstPipe.read() says 'I am the second pipe\n'
firstPipe.fileno()== 3
secondPipe.fileno()== 3

case 2:
 (Read 'I am the first pipe\n' from pipe)
 (pipe closing. fd== 3 )
 (Read '' from pipe)
secondPipe.fileno()== 3
dispatcher.secondPipe.read() says
Traceback (most recent call last):
  File "file_dispatcher_bug.py", line 77, in ?
    print "dispatcher.secondPipe.read() says",
repr(dispatcher.secondPipe.read())
IOError: [Errno 9] Bad file descriptor
[djh900@dh djh900]$