chrahunt/subprocess-check

subprocess-check

Provides a wrapper that traces sub-process output, if captured.

Uses

Easier debugging when capturing output in a sub-process call

Before:

import subprocess

result = subprocess.run(
    "echo error message >&2 && exit 1", shell=True, capture_output=True, check=True
)

Since the stderr output of the sub-process has been captured, we only see the command and exit code:

$ python t.py
Traceback (most recent call last):
  File "t.py", line 3, in <module>
    result = subprocess.run(
  File "lib/python3.8/subprocess.py", line 512, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command 'echo error message >&2 && exit 1' returned non-zero exit status 1.

After:

import subprocess

from subprocess_check import output_in_errors

with output_in_errors():
    result = subprocess.run(
        "echo error message >&2 && exit 1", shell=True, capture_output=True, check=True
    )

The stdout/stderr is traced right next to the exit code and command:

$ python t.py
Traceback (most recent call last):
  File "t.py", line 6, in <module>
    result = subprocess.run(
  File "lib/python3.8/site-packages/subprocess_check/_util.py", line 108, in wrap_subprocess_exception
    raise CalledProcessErrorWithOutput(exc_value).with_traceback(tb) from None
  File "lib/python3.8/subprocess.py", line 512, in run
    raise CalledProcessError(retcode, process.args,
subprocess_check._util.CalledProcessErrorWithOutput: Command 'echo error message >&2 && exit 1' returned non-zero exit status 1. Output captured:
 stdout: None
 stderr:
  error message

Alternatives

1. Manual error handling/formatting:
   • ➕ customizable formatting
   • ➕ no dependencies
   • ➖ ad-hoc code may not be tested as thoroughly
2. Don't capture stderr:
   • ➕ no dependencies
   • ➖ output to terminal in non-error case may be verbose, if sub-process stderr outputs regardless
   • ➖ if the error is re-raised after other operations, which output corresponds to the failed sub-process may not be nearby, or obvious
3. Wrap subprocess.run instead of using a context manager
   • ➕ no need to pass capture_output=True, check=True
   • ➖ IDEs do not understand "transparent function wrappers" well, so autocomplete and type hints are compromised