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Mar 9th, 2006

os.popen

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

Python Syntax (Toggle Plain Text)
>>> a = os.popen("netstat")
>>> for line in a.readlines():
	print line
 
Active Connections
 
>>>
>>> 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.

thanks

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a1eio

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Mar 14th, 2006

Re: os.popen

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

python Syntax (Toggle Plain Text)
# 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
[/php]
 ... and this ...
[php]# 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)
else:
  winflag = 1
  import winsound
  winsound.PlaySound(soundFile, winsound.SND_FILENAME)
# 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
[/php]
 ... and this ...
[php]# 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)
else:
  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.

Last edited by vegaseat; Oct 1st, 2009 at 4:40 pm. Reason: fixed code tags

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DaniWeb's Hypocrite

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Mar 14th, 2006

Re: os.popen

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

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Mar 15th, 2006

Re: os.popen

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

Python Syntax (Toggle Plain Text)
import os 
os.popen('program').write('whatever')
import os 
os.popen('program').write('whatever')

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Mar 15th, 2006

Re: os.popen

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

Python Syntax (Toggle Plain Text)
popen('start command.com').write('echo test')
popen('start command.com').write('echo test')

something similiar to that?

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Mar 16th, 2006

Re: os.popen

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.

alc6379

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Mar 16th, 2006

Re: os.popen

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

Python Syntax (Toggle Plain Text)
a = os.popen("cmd","w")
a.write("bla")
a = os.popen("cmd","w")
a.write("bla")

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

and yea i can imagine it is from the program.

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Mar 17th, 2006

Re: os.popen

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?

Last edited by alc6379; Mar 17th, 2006 at 4:13 am. Reason: speeling

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Mar 17th, 2006

Re: os.popen

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.

Python Syntax (Toggle Plain Text)
>>> 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
>>>
>>> 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

a1eio

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Mar 17th, 2006

Re: os.popen

Try to run this ...

Python Syntax (Toggle Plain Text)
import os
a = os.popen("cmd","w")
print a  # test
a.write('echo test')
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"?

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