Python's subprocess with "1>&2" and stderr=STDOUT -

i have code https://pymotw.com/2/subprocess/

i'm not sure how interpret code, in check_output 1>&2 output redirected stderr, in parameter, stderr stdout stderr=subprocess.stdout.

output = subprocess.check_output(     'echo stdout; echo stderr 1>&2; exit 1',     shell=true,       stderr=subprocess.stdout,      ) print "*****************" print 'have %d bytes in output' % len(output) print output 

running code, print commands not executed meaning nothing captured.

what code trying accomplish?

edit

from answer , comment, run code

try:     output = subprocess.check_output(         'echo stdout; echo stderr 1>&2; exit 1',         shell=true,  # no such file or directory error without, maybe 1>&2 requires shell=true         stderr=subprocess.stdout,           )  except subprocess.calledprocesserror e:      print "*****************"     print 'have %d bytes in output' % len(e.output)     print e.output 

this output:

***************** have 20 bytes in output stdout stderr 

however, when commented out stderr=subprocess.stdout line, got instead

to stderr ***************** have 10 bytes in output stdout 

edit2

i tested more stderr library (https://github.com/sickill/stderred) helps shell show characters stderr in red color.

when execute code (comment out redirection), can see to stderr in black color implies uses stdout.

output = subprocess.check_output(         'echo stdout; echo stderr 1>&2; exit 1',         shell=true,           #stderr=subprocess.stdout,          ) 

from this, guess (correct me if i'm wrong) python's check_output method prints out data stderr redirect stdout prints out error message stderr.

the 1 >&2 shell code applies (echo) command appears on. how tell shell direct output of echo shell's stderr stream.

the python code stderr=subprocess.stdout tells subprocess module want process's stderr stream same file descriptor stdout stream read whatever process writes either stream interleaved in 1 stream.

the exit 1 in shell command means shell exits error (non-zero) status.

the purpose of code demonstrate python function subprocess.check_output check exit status , raise exception when non-zero.

if exit code non-zero raises calledprocesserror. calledprocesserror object have return code in returncode attribute , output in output attribute.

your description of:

running code, print commands not executed

is bit misleading since neglect mention output occur:

traceback (most recent call last):   file "t.py", line 6, in <module>     stderr=subprocess.stdout,    file "/usr/lib/python2.7/subprocess.py", line 573, in check_output     raise calledprocesserror(retcode, cmd, output=output) subprocess.calledprocesserror: command 'echo stdout; echo stderr 1>&2; exit 1' returned non-zero exit status 1