subprocess pipe question

[Rita]

I have a process like this,

def run(cmd):
  #cmd=a process which writes a lot of data. Binary/ASCII data
  p=subprocess.Popen(cmd,stdout=subprocess.PIPE)

I would like to get cmd's return code so I am doing this,

def run(cmd):
  p=subprocess.Popen(cmd,stdout=subprocess.PIPE)
  rc=p.poll()
  print rc # and I get 'None' regardless of what cmd gives me (0 thru 255
are valid return codes)
  return p.stdout


When using wait() it works a bit better but not consistent
def run(cmd):
  p=subprocess.Popen(cmd,stdout=subprocess.PIPE)
  rc=p.wait()
  print rc
  return p.stdout

When the output of cmd is a small ascii file it works perfectly fine, but
when the file is large (more than 2MB) the process just waits for ever (I am
guessing its blocking?).  When I use the communicate call it works perfectly
but my process is consuming way too much memory.

Is there a better way to get my return code consistently efficiently and not
take up so much memory?







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