You don't need Snipmate for that. Save your header to a file, then add the following to your .vimrc
:
au BufNewFile *.py 0r /where/you/saved/your/header.template
This inserts your header automatically for every .py
file.
If you want a header with variables (e.g. changing dates, revision numbers, filenames, etc.), see this article and this for further help. But there are other plugin(s) to help you out.