NumPy is the most important library in any computational task in Python. It combines the ease and flexibility of scripting with very high performance. It is the most basic library used in any analytics or machine learning task in Python. Anyone interested in doing some real work in Machine Learning (not just talking about it), must be conversant with this library.

This is just a top level overview of the library. A developer should make all attempts to master this library. Unfortunately their documentation is not so good. There is a limit to tutorials and videos. I would recommend NumPy Cookbook - by Ivan Idris for someone who is genuinely interested in mastering the code.