As the title, I want to use markdown as my main write format and I need to generate PDF files from markdown using pure python.
I have done and would do it in two steps. First, I'd use python-markdown to make HTML out of my Markdown, and then I'd use xhtml2pdf to make a PDF file.
Edit (2014):
If I were doing this now, I might choose WeasyPrint as my HTML-to-PDF tool; it does a beautiful job, and I've used it on a couple projects recently.