Describe your environment

• Operating system: Ubuntu 18.04
• Python Version: 3.6.9
• CCXT version: 1.30.48 (pip freeze | grep ccxt)
• Freqtrade Version: 2020.6 (freqtrade -V or docker-compose run --rm freqtrade -V for Freqtrade running in docker)

Note: All issues other than enhancement requests will be closed without further comment if the above template is deleted

According to @rspadim, functions in entropy.py could use numpy array instead of strings, as it's better to numba.

Guide on how to implement this is available in the comments in PR #311 .

With Python 3.5.x having reached its end of life/support, we can (drop supposed 3.4 support 😆 and) begin to use "advanced" features from Python 3.6:

• f-strings
• [variable annotations](https://docs.python.org/3