os.popen

[Bart Nessux]

P at draigBrady.com wrote:
> Bart Nessux wrote:
> 
>> When using os.popen, at what point is the process actually started? 
>> Take the example below... would the first or second line actually 
>> execute the command? If it's the first line, then why would I want to 
>> use the second line at all unless I wanted to see on the console what 
>> happened?
>>
>> ping = os.popen('sh ./ping.sh')
> 
> 
> this will run until the buffer between the ping process and the python
> app is full. This is 4k under linux. Then the ping process will block
> until data is read as there is no where to put it's output.
> 
>> ping.read()
> 
> 
> This will read what's currently in the buffer between the processes.
> You will need to do this in a loop.
> 
> alternatively if you don't care about the output then you
> can throw it away, and hence remove the need for the ping.read() like:
> 
> ping = os.popen("sh ./ping.sh > /dev/null")
> 
>  > ping.close()
> 
> This will wait for the ping process to finish.
> 
> To tell it to finish you will need to do something like:
>   ping = popen2.Popen3("sh ./ping.sh > /dev/null")
>   os.kill(ping.pid, signal.SIGTERM)
>   ping.wait()
> 

Thank you for that explanation. It makes sense. When you say loop the 
read do you mean something like this:

ping = os.popen('sh ./ping.sh')
while 1:
    ping.read()
ping.close()

I liked the /dev/null examples too as I don't need output from some of 
the functions. I didn't know I could throw output away like that.

Thanks,
Bart