It would be nice if we could send output from subprocess.Popen objects
to any object with a write() method.

Consider the following example, where I'm using Python 2.4.4 (#1, Jun 28
2007, 15:10:17, GCC 3.4.3 on linux2)...

>>>
>>> fh = open('/tmp/file.txt', 'w')
>>> cmdObj = subprocess.Popen('uname -a', shell=True, stdout=fh)
>>> fh.close()
>>> fh = open('/tmp/file.txt', 'r')
>>> fh.read()
'Linux northstar 2.6.9-42.0.2.IT111843.1.ELsmp #1 SMP Fri May 11
18:50:54 EDT 2007 x86_64 x86_64 x86_64 GNU/Linux\n'
>>>

That demonstrates that I can successfully send the stdout output from my
subprocess.Popen object to a file handle.

I tried to send that output to a custom object that has a write() method...

>>>
>>> class Foo(object):
...     def write(self, msg):
...         sys.stdout.write('*** %s ***' % msg.rstrip() + os.linesep)
...         sys.stdout.flush()
...     def close(self):
...         pass
...
>>>
>>> foo = Foo()
>>>
>>> cmdObj = subprocess.Popen('uname -a', shell=True, stdout=foo)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/rel/lang/python/2.4.4-4/lib/python2.4/subprocess.py", line 534,
in __init__
    (p2cread, p2cwrite,
  File "/rel/lang/python/2.4.4-4/lib/python2.4/subprocess.py", line 840,
in _get_handles
    c2pwrite = stdout.fileno()
AttributeError: 'Foo' object has no attribute 'fileno'
>>>

so I gave it a fileno() method that returns None...

>>>
>>> class Foo(object):
...     def write(self, msg):
...         sys.stdout.write('*** %s ***' % msg.rstrip() + os.linesep)
...         sys.stdout.flush()
...     def close(self):
...         pass
...     def fileno(self):
...         return None
...
>>>
>>> foo = Foo()
>>>
>>> cmdObj = subprocess.Popen('uname -a', shell=True, stdout=foo)
>>> Linux northstar 2.6.9-42.0.2.IT111843.1.ELsmp #1 SMP Fri May 11
18:50:54 EDT 2007 x86_64 x86_64 x86_64 GNU/Linux
>>>

Notice that the output went straight to the console and bypassed my
'foo' object's write() method.

It's not going to be easy and there is also no point to implement the
feature. The subprocess module requires either a real file or a PIPE. A
real file is needed because the subprocess module uses some low level
operation system functions for speed efficiency. It writes data directly
to a file descriptor (the number returned by fileno()).

In your case it seems have to interpreted None as 0 which is - by
accident - the file descriptor of stdout.

For small amounts of data use Popen(..., stdout=subprocess.PIPE) and use
out, err = communicate([stdin]), for large amounts of data you should
use a temporary file (tempfile module).

In your case please use the platform module instead of uname :)