i don't understand the use of the os.popen function, i've used it to read things, for example:

>>> a = os.popen("netstat")
>>> for line in a.readlines():
	print line


Active Connections


i understand that, but there is also a buffersize and a write ability, but i've played about with it and i keep getting error's and stuff, i'm wondering if someone happens to know anything about the writing ability, i was thinking it would be cool if i could open some kind of pipe and write to it.


Recommended Answers

All 11 Replies

I looked around in code I had written and could only find these two examples ...

# pipe calendar.prmonth(2005, 6) to a string
# save the short code within the triple quotes as cal_mar2006.py:
import calendar
calendar.prmonth(2006, 3)

import os

# give full path of .py file so python.exe can find it
p = os.popen("python D:/Python24/Atest/cal_mar2006.py")
# pipe the output to string str1
str1 = p.read()
print str1

... and this ...

# play a sound file, linux or windows choice:
import sys

# pick a soundfile you have ...
soundFile = "D:/Python24/Atest/Sound/game_over.wav"

if sys.platform[:5] == "linux":
  winflag = 0
  import os
  os.popen2("aplay -q " + soundFile)
  winflag = 1
  import winsound
  winsound.PlaySound(soundFile, winsound.SND_FILENAME)

os.popen() behaves similar to a file open(), the default is "r" for read, so for write to have to addd a "w". You can specify the buffer size in bytes or use the default of zero.

yea i kinda got that it's the write bit i'm interested in, and i havn't managed to actually write anything without getting an error, lol i'll play with it

What is the command/program you want to write to?
You could use something like ...

import os 

i was thinking msdos, as in i do summit simple to test like:

popen('start command.com').write('echo test')

something similiar to that?

What little I know, your Python code looks correct. But, why the "start" part of command.com?

I know you can't really spawn new programs in DOS, but other than that it looks ok. It looks like you just use the write() method to provide input to whatever program, and that program has to accept input from stdin. I would imagine that's where your errors are coming from-- not from Python, but from the actual program that you're using os.popen() on.

yea i know, i could have just done 'start' or 'cmd' or something like that but it's the write bit where i get problems, all other cases i get an error EXCEPT for if i use

a = os.popen("cmd","w")

that gives me no error, but i also see f*all

and yea i can imagine it is from the program.

What exactly is the program you're running, and what is the error you're getting?

If you can give the exact statements you're using, maybe we could provide some more help.

If creating an object like you demonstrated causes no issue, why not just run with it that way?

i was just messing about, not really making anything, i have this little script i run at school to tell me when the teacher turns the monitoring software on, it basically does a netstat and checks for the port, but i have to keep opening a netstat pipe, i just thought it would maybe be faster if i just opened a dos shell through python and kept sending the same command. nothing really important i was just intreeged about the write part but i could never get it working.

>>> import os
>>> a = os.popen("cmd","w")
>>> a.write('echo test')

Traceback (most recent call last):
  File "<pyshell#2>", line 1, in -toplevel-
    a.write('echo test')
IOError: [Errno 22] Invalid argument

IOError: [Errno 22] Invalid argument is the error i tend to get all the time

cheers for the help :)

Try to run this ...

import os
a = os.popen("cmd","w")
print a  # test
a.write('echo test')

Also what happens if you give it the full path of cmd.exe, or replace "cmd" with a program that does not exist like "cmdxxx"?

perhaps you need to use " " instead of ' ' quotes?

perhaps you need to use " " instead of ' ' quotes?

I think Python accepts either " or ' as long as they match.

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.