This is a Vim plugin that opens file.py if you've asked it to edit file. If file exists or file.py doesn't, it does not interfere. By default supported extensions are .go, .py, .js and .html, but you may change them by setting g:ext_completer_extensions to you preferred list of values, e.g.

let g:ext_completer_extensions = ["py", "go", "txt"]

To install this plugin, first install Vundle and then add

Plugin 'rryk/ext-completer'

to your .vimrc.