If you encounter the error "No module named 'unittest.mock'" when running a program that uses PyTorch, it typically indicates that your Python environment may be configured incorrectly or that you are using an older Python version that does not support this module. unittest.mock is a module for mocking objects in unit tests, available in Python 3.3 and later versions. To resolve this issue, first confirm that your Python version is at least 3.3 and check if your environment variables (such as PYTHONPATH) are set correctly. If the problem persists, consider using a virtual environment (like venv or conda) to avoid conflicts between libraries and ensure that the PyTorch version you have installed is compatible with your Python version. Additionally, although unittest.mock was deprecated in Python 3.8, it remains usable, and you can import it via from unittest import mock. If possible, updating your code to utilize the latest features and best practices of Python is also recommended.