In 2014, I was first introduced to pandas and had no idea how to use it. By 2017, I had written the 500 page book Pandas Cookbook. This is roughly the path I took to mastering pandas for free:

1. Read the official documentation
2. Practice examples in the documentation
3. Flashcards
4. Share a full data analysis with others
5. Answer old Stack Overflow Questions
6. Answer new Stack Overflow Questions
7. Teach others in-person or online
8. Write pandas blog posts
9. Repeat

Read the official documentation

The...