Executing External Commands with Python Subprocess

This challenge focuses on mastering Python's subprocess module, a crucial tool for interacting with the operating system by running external commands and programs. You'll learn how to reliably execute commands, capture their output, and handle potential errors, which is fundamental for automating tasks and integrating with other system tools.

Problem Description

Your task is to create a Python script that executes a given external command using the subprocess module. The script should accept the command as a list of strings (where the first element is the command itself and subsequent elements are its arguments). It needs to capture both the standard output and standard error of the executed command.

Key Requirements:

1. Execute Command: Use a function from the subprocess module (e.g., subprocess.run) to execute the provided command.
2. Capture Output: Capture the standard output (stdout) of the command.
3. Capture Errors: Capture the standard error (stderr) of the command.
4. Handle Non-Zero Exit Codes: If the executed command returns a non-zero exit code (indicating an error), the script should raise a RuntimeError with a descriptive message including the command that failed and its stderr.
5. Return Values: The function should return a tuple containing the captured stdout and stderr as strings.

Expected Behavior:

• Successful execution of a command should return its stdout and stderr.
• An unsuccessful execution (non-zero exit code) should raise an exception.

Edge Cases to Consider:

• Commands with no arguments.
• Commands that produce output on both stdout and stderr.
• Commands that produce no output.
• Commands that are not found by the system. (While subprocess.run will raise a FileNotFoundError for this, your RuntimeError handling should also be robust).

Examples

Example 1:

Input command: ["echo", "Hello, Subprocess!"]

Output:
("Hello, Subprocess!\n", "")

Explanation: The echo command successfully executes and prints "Hello, Subprocess!" to stdout. There is no output to stderr.

Example 2:

Input command: ["ls", "-l", "/non_existent_directory"]

Output:
(Raises RuntimeError)

Explanation: The ls -l command is executed with an invalid path. The operating system returns an error message to stderr, and the command exits with a non-zero status. The script should catch this and raise a RuntimeError containing the error message from stderr. (The exact stderr content might vary slightly based on the OS, but it will indicate an error like "No such file or directory").

Example 3:

Input command: ["python", "-c", "import sys; sys.stderr.write('Error message\\n')"]

Output:
("", "Error message\n")

Explanation: This command directly writes to stderr and produces no stdout. The script correctly captures the stderr content.

Constraints

• The input command will always be a list of strings.
• The script should be written in Python 3.
• For performance, avoid unnecessary copying of large output strings.
• Assume the Python environment has access to standard system commands like echo, ls, and the python interpreter itself.

Notes

• Consider using subprocess.run() with capture_output=True, text=True, and check=False for efficient capture and decoding of output.
• Remember that text=True automatically decodes the output using the default encoding. If you need to handle specific encodings, you might omit text=True and decode manually using .stdout.decode() and .stderr.decode().
• Raising a RuntimeError is a common Pythonic way to signal an unexpected failure during runtime.
• The subprocess.run function is generally preferred over older functions like subprocess.call or subprocess.Popen for simpler use cases like this one.