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[Python] - subprocess issue

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# 1  
Old 09-18-2019
[Python] - subprocess issue
So I have this basic script, see below

Code:
import subprocess
import shlex

command = "gcloud projects list"

subprocess.check_output(shlex.split(command))
subprocess.check_call(shlex.split(command))

The subprocess.check_call(shlex.split(command)) actually return what I expect. It returns the result of gcloud projects list. However subprocess.check_output doesn't, in fact it returns nothing.

Can explain this?
Last edited by Neo; 09-19-2019 at 12:56 AM.. Reason: Added icode tags to discussion
# 2  
Old 09-18-2019
My understanding is the operation of the two are different:

Documentation -
Quote:
check_call() returns as soon as /bin/sh process exits, it does not wait for child processes to complete

check_output() waits until all output is read. When (and if) check_output inherits the stdin pipe then check_output() will wait until it exits, i.e., until the child process the inherited pipe. In other words it waits for the child process to end.
Try getting get rid of the shlex,
Code:
subprocess.check_output( [ "command" "parameter_1" ])

# 3  
Old 09-18-2019
It is also possible that the command that you are running is sending the output to stderr instead of stdout

Try this instead:-

Code:
subprocess.check_output(shlex.split(command), stderr=subprocess.STDOUT)

# 4  
Old 09-18-2019
Quote:
Originally Posted by jim mcnamara
My understanding is the operation of the two are different:

Documentation -


Try getting get rid of the shlex,
Code:
subprocess.check_output( [ "command" "parameter_1" ])

That's not going to work. I need the shlex and even if I didn't have it, it still wouldn't work.
# 5  
Old 09-18-2019
Quote:
Originally Posted by Yoda
It is also possible that the command that you are running is sending the output to stderr instead of stdout

Try this instead:-

Code:
subprocess.check_output(shlex.split(command), stderr=subprocess.STDOUT)

That doesn't work etiher. Also the exact same command works with subprocess.check_call. What's weird is the subprocess.check_output works in the python shell but not from the python script.
# 6  
Old 09-18-2019
To see the output from program, you have to print the output. I believe stdout is used internally for this function:-

Code:
print subprocess.check_output(shlex.split(command))

This User Gave Thanks to Yoda For This Post:
scj2012
# 7  
Old 09-18-2019
Quote:
Originally Posted by Yoda
To see the output from program, you have to print the output. I believe stdout is used internally for this function:-

Code:
print subprocess.check_output(shlex.split(command))

That does work. Why does it work from the python shell without print?

Also I looked at 17.1. subprocess — Subprocess management — Python 2.7.16 documentation and it doesn't mention anything about having to do a print.
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