**Course Title:** Modern Python Programming: Best Practices and Trends **Section Title:** Automation and Scripting **Topic:** Interacting with system processes using `subprocess` and `os` modules. **Introduction** In this topic, we'll explore how to interact with system processes using Python's `subprocess` and `os` modules. These modules provide a way to execute system commands, manage processes, and access environment variables, making it easier to automate tasks and integrate your Python scripts with the operating system. **Understanding the `subprocess` Module** The `subprocess` module allows you to spawn new processes, connect to their input/output/error pipes, and obtain their return codes. This module is a replacement for the `os` module's `popen()` and `system()` functions. Here's a basic example of using the `subprocess` module to execute a system command: ```python import subprocess # Execute a system command result = subprocess.run(['ls', '-l']) # Print the output print(result.stdout) ``` In this example, we use the `subprocess.run()` function to execute the `ls -l` command. The `run()` function returns a `CompletedProcess` object, which contains information about the executed process, including the output, error, and return code. **Using the `subprocess` Module to Execute Shell Commands** You can also use the `subprocess` module to execute shell commands. To do this, you need to pass the `shell=True` argument to the `subprocess.run()` function. Here's an example: ```python import subprocess # Execute a shell command result = subprocess.run('ls -l', shell=True) # Print the output print(result.stdout) ``` However, be careful when using `shell=True`, as it can introduce security risks if you're passing untrusted input to the shell. **Working with the `os` Module** The `os` module provides a way to use operating system-dependent functionality. This includes working with environment variables, managing processes, and accessing the current working directory. Here's an example of using the `os` module to get the current working directory: ```python import os # Get the current working directory cwd = os.getcwd() # Print the current working directory print(cwd) ``` You can also use the `os` module to set and get environment variables. Here's an example: ```python import os # Set an environment variable os.environ['MY_VAR'] = 'my_value' # Get an environment variable var = os.environ['MY_VAR'] # Print the environment variable print(var) ``` **Using the `subprocess` and `os` Modules Together** You can use the `subprocess` and `os` modules together to execute system commands and access environment variables. Here's an example: ```python import subprocess import os # Set an environment variable os.environ['MY_VAR'] = 'my_value' # Execute a system command result = subprocess.run(['echo', '$MY_VAR'], shell=True) # Print the output print(result.stdout) ``` In this example, we set an environment variable using the `os` module and then use the `subprocess` module to execute a shell command that echoes the value of the environment variable. **Practical Takeaways** * Use the `subprocess` module to execute system commands and manage processes. * Use the `os` module to access environment variables, manage processes, and access the current working directory. * Be careful when using `shell=True` with the `subprocess` module, as it can introduce security risks. * Use the `subprocess` and `os` modules together to execute system commands and access environment variables. **External Resources** * [Python `subprocess` module documentation](https://docs.python.org/3/library/subprocess.html) * [Python `os` module documentation](https://docs.python.org/3/library/os.html) **What's Next?** In the next topic, we'll explore how to work with Python for network automation and web scraping. **Leave a Comment or Ask for Help** If you have any questions or need help with any of the concepts covered in this topic, please leave a comment below.