Which library is used to retrieve the current working directory?

The library that is used to retrieve the current working directory is the os library. This library provides a way for Python to interact with the operating system, and it includes various functions to handle directory and file management. Specifically, the os.getcwd() function returns a string representing the current working directory of the process, making it easy to determine where your script is operating within the file system.

The other libraries mentioned serve different purposes: the pdb library is focused on debugging, providing tools to help developers troubleshoot code; urllib is used for handling URLs and making HTTP requests, primarily for web-related tasks; and sys is a module that provides access to variables and functions that interact directly with the Python interpreter, such as command-line arguments. Therefore, while these libraries have their specific uses, only the os library is equipped to manage file and directory operations, including obtaining the current working directory.