[Tutor] Fwd: print a for loop system call

[Alan Gauld]

On 20/01/18 18:26, Derek Smith wrote:

> import os
> import sys
> from subprocess import Popen, PIPE
> 
> pipe = Popen('lsdev -c tape', shell=True, stdout=PIPE)
> 
> for dev in pipe.stdout :
>     print ( dev.strip().split()[0].decode() )    ## A ##

This is OK

>     # print ( dev.strip().split().decode()[0] ) ## B ##

This tries to decode a list which won't work.
split() returns a list.
You want to apply decode to a string,
specifically the first string that split produces,
so it is correct as in option A.

If in doubt split the line up and print each
component as you create it:

for dev in pipe.stdout :
    print( dev.strip() )
    print( dev.strip().split())
    print( devb.strip().split()[0])
    print( dev.strip().split()[0].decode() )



> And if I try to store in an array using
> 
> rmts = [ dev.strip().split()[0].decode() ]
> 
> it only stores the last line when there are over 100 lines.

Wrong, it stores every line as it comes to it.
But, since you create a new list each time you
throw way the previous one. Only the last list
is preserved, but they were all stored, albeit
briefly...

You need to append() to a list, something like:

aList = []
for dev in....
   process dev
   aList.append(result)

Or as a list comprehension:

aList = [process(dev) for dev in ....]

-- 
Alan G
Author of the Learn to Program web site
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