The essentials of Python in a handy Quick Reference with comprehensible code examples and intuitive navigation.
Not for learning, just for reference.
Document as of: October 4, 2019 (incomplete)
Python Version: 3.7.3
Without further requirements you can view the Python - Quickreference via the Notebook Viewer (you won't be able to execute code here).
If you want to execute code you can run the Notebook also on Binder.
You can find the ipynb-source-file of this Jupyter Notebook here on my GitHub. You will have to download or clone it, then run it in Jupyter's Software (Notebook or Lab). First you have to get yourself a Python installation, of course (if not already installed). If you are going to do Data Science my recommendation is Anaconda. It comes with a Python installation, as well as Jupyter Notebook and Lab and many other features like a handy package manager.