Added characters to string when exiting subprocces

Question

I am calling a subprocess and returning a string if there is an error. Code example:

When calling the process:

def read_plan_with_break():
    comand = " python script.py "
    proc = subprocess.Popen(comand.split(), shell=False, stdout = subprocess.PIPE, stderr= subprocess.PIPE)
    if proc.wait() != 0:
        output, err = proc.communicate() 
        print (err)
        return "Error in subprocess"
    return True

when exiting the subprocess:

def fatal_error():
  print("Some message", file=sys.stderr)
  exit(1)

My problem is that the stderr output is : b'Some message\r\n' I can erase the \r\n with strip but have no idea why there is a b at the beginning and the ' at the start and the end.

Does anyone know why this occurs?

EDIT: I have tried err.split()[2:-1] to get rid of the b' but it cuts off the start of the Some message

If I get a down-vote, please explain so I can improve and make better questions in the future

It just means its a bytestring. You cant remove the `b` by substringing, its not part of the string. see [here](http://stackoverflow.com/questions/22824539/what-is-a-python-bytestring) — Paul Rooney, Nov 29 '16 at 02:54
@PaulRooney It si my first time hearing about bytestrings, i am new to python, thank you — kemis, Nov 29 '16 at 02:59

score 2 · Accepted Answer · answered Nov 29 '16 at 03:09

2

err is a bytestring, you should decode it first by err.decode(), this returns the string

answered Nov 29 '16 at 03:09

TheClonerx

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Added characters to string when exiting subprocces

1 Answers1