Python difference on subprocess run(), call(), check_call(), check_output()

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)
  res.stdout
  

• 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(
      capture_output=True,
      encoding="utf-8",
      check=True
  )
  # command = ["unknown_command", "-l"]
  # command = ["python", "-askjd"]
  command = ["ls", "-l"]
  
  try:
      # output type is subprocess.CompletedProcess
      output = subprocess.run(command, **default_run_params)
  
      # print in pure string in one line
      print(output)
  
      # print with new line just as launching from shell
      print(output.stdout)
  
      # 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}")
      raise
  except subprocess.CalledProcessError as exc:
      print(exc)  # no error details will given by print(exc)
      print(exc.__dict__)  # print all
      print(exc.returncode)
      print(exc.stderr)  # print error message only
      # exc.stdout should be empty
      raise