Singletoned/python.el — comment on commit 50e3524f333f6e9677cde52eab56c7ab7eb914c2
File:  line 0
By fgallina:

No man should use tabs in his python code, and as you see, later on the code this line is called:

(set (make-local-variable 'indent-tabs-mode) nil)

That kills tab usage for good so I don't think a more customizable tab-width is needed at all.