Simple file-renaming program in python
Try using pathlib over os when you're dealing with file/glob operations. It has a lot cleaner interface, and is part of standard library in python 3.
Name constants in your code with the CAPITAL_SNAKE_CASE. It is recommended guideline from the PEP-8.
Split your code into individual functions doing a single task each.
Put the execution flow for your code inside an if __name__ == &quot;__main__&quot; block.