Why sometimes Python subprocess failed to get the correct exit code after running a process?

Question

I am using Python subprocess to run external scripts on Windows 7. I am trying to get the exit code.

---

In case 1, I run a python script test1.py.

test1.py

import sys
sys.exit(24)   <--exit code

myscript1.py

import subprocess
process = subprocess.Popen(["python", "C:\\path\\to\\test1.py"], stdout=subprocess.PIPE)
process.wait()
print process.returncode

In Windows command prompt, when I run the script, I get the following output:

>python test1.py
>
>echo %errorlevel%
>24
>
>python myscript1.py
>24

So, you can see that subprocess is able to get the correct exit code in this case.

---

In case 2, I run a batch file test2.cmd.

test2.cmd

EXIT /B 56   <--exit code

myscript2.py

import subprocess
process = subprocess.Popen(["C:\\path\\to\\test2.cmd"], stdout=subprocess.PIPE)
process.wait()
print process.returncode

In Windows command prompt, when I run the script, I get the following output:

>test2.cmd
>
>echo %errorlevel%
>56
>
>python myscript2.py
>56

So, you can see that subprocess is also able to get the correct exit code in this case.

---

In case 3, I run a SikuliX script.

test3.sikuli

xxx xxx (sikuli script here)
xxx xxx
...
exit(16)   <--exit code

myscript3.py

import subprocess
process = subprocess.Popen(["C:\\path\\to\\runsikuli.cmd", "-r", "C:\\path\\to\\sikuli-script.sikuli"], stdout=subprocess.PIPE)
process.wait()
print process.returncode

In Windows command prompt, when I run the script, I get the following output:

>C:\path\to\runsikuli.cmd -r C:\path\to\sikuli-script.sikuli
>... (stdout + stderr)
>16
>
>echo %errorlevel%
>16
>
>python myscript3.py
>0

In case 3, when I run the script manually in the command prompt, it is able to set the %errorlevel%. When I run the script using Python subprocess, subprocess is unable to get the correct exit code. It always return 0.

Why Python subprocess failed to get the exit code in case 3?

Answer 1

As your comment says if you run the same command then both the command prompt and using Python subprocess module produce the same result (0 exit code).

You may see different exit codes because you use different commands. No surprise here. Python subprocess module returns correct (for a given command) exit code.

---

If it doesn't return the right exit status then you could add & exit at the end of your cmd.exe command as a workaround to get the correct return code, see "subprocess on Windows: wrong return code with shell=True" on Python issue tracker:

from subprocess import check_call

check_call(r'C:\path\to\runsikuli.cmd -r C:\path\to\sikuli-script.sikuli & exit',
           shell=True)