Subprocess

Introduction

Subprocess allows spawning external processes and interacting with system commands.

Basic Execution

import subprocess

# Run command
result = subprocess.run(["ls", "-la"], capture_output=True, text=True)
print(result.stdout)
print(result.stderr)

# Shell command
result = subprocess.run("ls -la", shell=True, capture_output=True)

Working with Output

import subprocess

# Get output as string
result = subprocess.run(["python", "--version"], capture_output=True, text=True)
print(result.stdout)

# Check return code
result = subprocess.run(["ls", "nonexistent"])
print(result.returncode)  # 2

# Raise on non-zero exit
try:
    subprocess.run(["ls"], check=True)
except subprocess.CalledProcessError as e:
    print(f"Command failed: {e}")

Async Execution

import subprocess

# Popen for async
process = subprocess.Popen(["python", "-c", "import time; time.sleep(5)"])
process.wait()  # Wait for completion
process.terminate()  # Kill process

Practice Problems

1. Run system commands from Python
2. Capture command output
3. Handle command errors
4. Use Popen for async processes
5. Pipe commands together