Did you search the topic of the forum?
Check link:
In readme you will find a few links
others version of python doesnt work.
Do not forget to install the java.

start,open CMD (command line),enter:
python -m pip install mitmproxy
or specific version packpage: (ver0.12 - 0.18 for python2.7 /ignore python3.5 -not supported mitmproxy v2.0.2)
python -m pip install mitmproxy==0.14 # specific version
I do not remember exactly which versions of mitmoproxy worked NFSworld.
You must try several versions of Mitmproxy. I remember that some higher versions did not work properly.
Version1.9.3 = It is not dependent on python