CODEWITHSUNDEEP
pythonbashexceptionerror-handling
kramer65
kramer65

Reputation: 54013

How to know the exact output from a Python subprocess.check_output() call?

I'm running some terminal commands from within Python using the subprocess.check_output() call. This works all fine when it returns correct results. When interacting with the bitcoin daemon I can get several responses however. For example, the raw output (as seen on a normal bash command line) can be:

: Cannot obtain a lock on data directory /home/kramer65/.bitcoin. Bitcoin is probably already running.

or

error: couldn't connect to server

Both these responses give an error code 1 however. I tried printing out the following attributes of the subprocess.CalledProcessError as e, which in both cases results in the same outputs (except for the cmd attribute of course:

print e.args, e.cmd, e.message, e.output, e.returncode
#       ()   'BTC'                            1
#       ()   'BTC getinfo'                    1

I guess the only thing that distincts the two errors, is the raw string that is outputted on the command line which I listed above. So my question is: how can I get the raw string that is shown on the command line from within Python?

Upvotes: 3

Views: 453

Answers (1)

wim
wim

Reputation: 363566

It is likely coming on the stderr.

You could setup your subprocess with

stderr=subprocess.STDOUT

as a kwarg to merge the stdout and stderr together.

Alternatively, if you need them separately, do something like

proc = subprocess.Popen(..., stdout=subprocess.PIPE, stderr=subprocess.PIPE)
stdout, stderr = proc.communicate()

Note: unlike check_output, this method will not raise exception if the return code was nonzero, so you will have to do that manually if that's the behaviour you wanted.

Upvotes: 3

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