What shell does Python's subprocess use?

Question

This question and answer demonstrates how to use Python's subprocess module to interact with bash from Python.

So if subprocess doesn't use the system's default shell, then what shell does it use to run commands like this:

    import subprocess

    print subprocess.check_output(["ls", "-la"])

Answer 1

If shell is not passed as a keyword argument it uses fork_exec, or _winapi.CreateProceess

• https://github.com/python/cpython/blob/f3751efb5c8b53b37efbbf75d9422c1d11c01646/Modules/_posixsubprocess.c#L600
• https://github.com/python/cpython/blob/f3751efb5c8b53b37efbbf75d9422c1d11c01646/Modules/_winapi.c#L1062
• https://github.com/python/cpython/blob/e02ab59fdffa0bb841182c30ef1355c89578d945/Lib/subprocess.py#L1770
• https://github.com/python/cpython/blob/e02ab59fdffa0bb841182c30ef1355c89578d945/Lib/subprocess.py#L1434

If shell=True:

• posix it uses /bin/sh, .
• windows it uses cmd.exe.

See:

• https://github.com/python/cpython/blob/master/Lib/subprocess.py#L1698-L1704
• https://github.com/python/cpython/blob/e02ab59fdffa0bb841182c30ef1355c89578d945/Lib/subprocess.py#L1421-L1425
• https://github.com/python/cpython/blob/e02ab59fdffa0bb841182c30ef1355c89578d945/Lib/subprocess.py#L1670