Python: async check_call

Question

How can one simulate the behavior of "subprocess.check_call" but with asyncio?

asyncio seems to provide only the method "asyncio.create_subprocess_shell", which is lower level.

Answer 1

It's actually quite simple to wrap create_subprocess_shell to act like check_call. From the specification in python docs:

Run command with arguments. Wait for command to complete. If the return code was zero then return, otherwise raise CalledProcessError. The CalledProcessError object will have the return code in the returncode attribute. If check_call() was unable to start the process it will propagate the exception that was raised.

So we can write this function

import asyncio
from subprocess import CalledProcessError

async def check_call(cmd, **kwargs):
    process = await asyncio.create_subprocess_shell(cmd, **kwargs)
    return_code = await process.wait()
    if return_code != 0:
        raise CalledProcessError(return_code, cmd)

so that in a case like this

async def main():
    await check_call("ls non_existing_path")

asyncio.run(main())

will print the following

ls: cannot access 'non_existing_path': No such file or directory
Traceback (most recent call last):
  File "73214383.py", line 13, in <module>
    asyncio.run(main())
  File "/usr/lib/python3.8/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "/usr/lib/python3.8/asyncio/base_events.py", line 616, in run_until_complete
    return future.result()
  File "73214383.py", line 11, in main
    await check_call("ls non_existing_path")
  File "73214383.py", line 8, in check_call
    raise CalledProcessError(return_code, cmd)
subprocess.CalledProcessError: Command 'ls non_existing_path' returned non-zero exit status 2.

which is quite similar to how python's check_call would behave.