CODEWITHSUNDEEP
pythonsubprocess
citron
citron

Reputation: 85

why 'DEVNULL' and 'PIPE' from 'subprocess' were printed as '-3' and '-1'?

Two values 'DEVNULL' and 'PIPE' for stdout and stderr respectively were printed as '-3' and '-1' when I put them into a dic. How to solve this problem except transform them into strings through adding '' symbols because they will be afterwards as arguments incorporated into a subprocess.run function.

from subprocess import DEVNULL, PIPE

F1 = DEVNULL
F2 = PIPE
L1 = {'stdout':F1, 'stderr':F2}

print(L1)

output

{'stdout': -3, 'stderr': -1}

Upvotes: 1

Views: 105

Answers (1)

Daweo
Daweo

Reputation: 36690

Everything is fine, if you look into subprocess source you will find that

Constants
---------
DEVNULL: Special value that indicates that os.devnull should be used
PIPE:    Special value that indicates a pipe should be created
STDOUT:  Special value that indicates that stderr should go to stdout

and

PIPE = -1
STDOUT = -2
DEVNULL = -3

Example:

import subprocess
subprocess.run(['echo', '123'], stdout=subprocess.DEVNULL)

is equivalent to

import subprocess
subprocess.run(['echo', '123'], stdout=-3)

but 1st is less cryptic for someone reading such code

Upvotes: 1

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