Python - How to search text files looking for a search phrase

https://github.com/dnishimoto/python-deep-learning/blob/master/9.%20Stackoverflow.ipynb

Machine learning and deep learning is the most important breakthrough in the 21st century. Companies around the world are in a race to automate replacing 85 million jobs in the next five years.

I search a directory looking for all files that end with the extension txt and then read all the lines of the text and search each line using a regular expresssion for a pattern