Please add #!/usr/bin/env python to top of every python file

[jonathanelscpt]

Hi,

I'm working through these on Ubuntu. It's a bit painful to have to add this to the top of every file. Can the repo be updated to include this? Perhaps could be included as part of #21?

Otherwise, I don't mind putting in a pull request myself.

Regards,
Jonathan

[annegentle]

I think we should be cautious before applying to all .py files - we can't know everyone's environment and we would need to indicate the python version as well.