on the page:

http://www.python.org/doc/2.3.4/lib/module-popen2.html

it lists os.popen4 return as:

Returns the file objects (child_stdout_and_stderr, child_stdin)

in practice it would appear to be (Solaris):

Returns the file objects (child_stdin,child_stdout_and_stderr)

Logged In: YES 
user_id=593130

You (understandably) confused two nearly identical but 
different functions with two different return conventions 
(reversed from each other). 

>>> from os import popen4
>>> popen4
<built-in function popen4>
>>> popen2.popen4
<function popen4 at 0x00898768>

Module-popen2.html talks about popen2.popen4 and not 
os.popen4.

 Module popen2 has 3 functions popen2/3/4 which 
consistently return the read and write pipes in that order 
(well, popen3 is more complicated, but never mind).

  The os module also has functions of the same name but 
with reversed return order -- in/out -- as documented:
"This functionality is also available in the popen2 module using 
functions of the same names, but the return values of those 
functions have a different order."

Why ther reversal?  No idea.

The same hint/warning currently does NOT appear in the 
popen2 doc nor in its doc string (as accessed via help()) and 
I agree it should be.

Suggestion to doc fixer: in Lib Ref 6.8 popen2, end of 4th 
paragraph, ending in " or the equivalent functions in the os 
module." --
Add "(with reversed return tuples)" before the period.  
Without this caveat, they are not really equivalent, as Chen 
tripped over.

Logged In: YES 
user_id=11375

I've added a note to the popen2 docs about this.