When I launch a python application with a gui on my macbook pro running fedora 21 - the tkinter gui is very small.
Is there any way I can scale this up so its useful?
Yes, see this question here.
You could also Google "python tkinter scale up DPI", which gives that as the second link.
Essentially, (as the other question outlines), you need a scaling factor. This is based around an idealised 72 DPI. So, for a 300 DPI display, you may wish to set a factor of around 4.0
(technically 4.166
):
root.tk.call('tk', 'scaling', 4.0)