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Difference on subprocess run(), call(), check_call(), check_output()

Since Python 3.5, the official doc explains that:

Prior to Python 3.5, these three functions (subprocess.call(), subprocess.check_call(), subprocess.check_output()) comprised the high level API to subprocess. You can now use subprocess.run() in many cases, but lots of existing code calls these functions.

subprocess.run common parameters

  • subprocess.run default behavior accepts arguments in list

    subprocess.run(["ls", "-l"])
  • shell=True (default False) to send arguments in string

    subprocess.run("ls -l", shell=True)
  • capture_output=True (default False) to save output in a var

    res = subprocess.run("ls -l", shell=True, capture_output=True)
  • encoding="utf-8" (default None) to save var in string instead of bytes.

  • check=True (default False) to raise subprocess.CalledProcessError: if command returned non-zero exit code. But if the command executable doesn’t exist for exampel missspellm you will get the error FileNotFoundError

  • Popen() is for advanced usage. For example, replacing the shell pipeline.

    shell command:

    output=$(dmesg | grep hda)

    with Popen, becomes:

    p1 = Popen(["dmesg"], stdout=PIPE)
    p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
    p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
    output = p2.communicate()[0]
  • default params

    import subprocess
    default_run_params = dict(
    # command = ["unknown_command", "-l"]
    # command = ["python", "-askjd"]
    command = ["ls", "-l"]
        # output type is subprocess.CompletedProcess
        output = subprocess.run(command, **default_run_params)
        # print in pure string in one line
        # print with new line just as launching from shell
        # as we catch error with `check=True`,
        # output.stderr is always an empty string.
        # and output.returncode is always 0 in this case.
    except FileNotFoundError as exc:
        print(f"{type(exc).__name__}: {exc}")
    except subprocess.CalledProcessError as exc:
        print(exc)  # no error details will given by print(exc)
        print(exc.__dict__)  # print all
        print(exc.stderr)  # print error message only
        # exc.stdout should be empty



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