SubProcess

Subprocess is a Python standard library module that enables spawning new processes, connecting to their input/output/error pipes, and obtaining their return codes. It was introduced as a more powerful and flexible replacement for older facilities such as os.system and os.popen. The module provides both a high-level API for simple tasks and a low-level interface for fine-grained control.

At the high level, the run function executes a command and returns a CompletedProcess instance containing the arguments, return code, and optionally stdout and stderr. For more detailed control, the Popen class allows creating a process, then communicating with it or reading its streams asynchronously. Additional helpers include check_call and check_output, which raise CalledProcessError on failure. Since Python 3.5, run has become the recommended entry point, with capture of output via capture_output=True or by setting stdout and stderr to subprocess.PIPE.

Usage considerations: by default, most functions do not invoke a shell; to run shell commands as a single string, shell=True may be used, but it introduces security risks such as shell injection. Prefer passing a sequence of program and arguments. To get text rather than bytes, enable text=True (or universal_newlines=True for older versions) and consider a timeout to avoid hang. The module supports environment manipulation with the env parameter and redirection of stdin/stdout/stderr.

Platform notes: subprocess works on Unix-like systems and Windows, with some path and quoting differences. Commands and environments that work on one platform might not on the other, so input validation is important. Errors raise subclass of CalledProcessError; callers can catch to implement error handling.