vim-flake8 is not working

pip install flake8

and if you run into permission errors:

sudo -H pip install flake8

If you installed flake8 already and that error occurred still, then call flake8 using absolute path.

To do this, edit line 73 of ~/.vim/autoload/flake8.vim as following:

call s:DeclareOption('flake8_cmd', '', '"/absolute/path/to/flake8"')

The error message is telling you that you didn't install the program flake8. Install it.

Assuming pip is installed

pip install flake8

should work.

If installing flake8 via pip is not working try this:

apt-get install flake8

Worked for me.