Maybe I am too late to share a solution here but it might help someone in the future.
i was also trying to setup YOLO and was trying for a complete one day to solve the VC++ error message.
Command i was trying to run: python setup.py build_ext --inplace
Error message everyone knows: Microsoft Visual C++ 14.0 is required
so i google it visit many forums and tried everything, from reinstalling VC++ tools for VS2015 many times and restart my system many times, set paths in environment variables.
but none worked for me...
what worked for me>>>>?
1: Install VC++ build tools from build-tools-for-visual-studio-2017, once you run the setup, check only Visual C++ build tools and select all important optional check boxes on the right side. it might take more than 8 GB on your desk, then restart your system.
2: Add path in Environment Variables to your VC that will be: C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC
3: Also add path to: C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools\VC\Tools\MSVC\14.15.26726 with variable name: VS140COMNTOOLS
4:Once its done type Native Tools in windows start menu. you should see X64 Native Tools Command Prompt for VS2017 click on it, it will open a command prompt, run your command again inside this command prompt not in regular windows command prompt.
I hope it will work for you.