set tabstop=4 " The width of a TAB is set to 4.
" Still it is a \t. It is just that
" Vim will interpret it to be having
" a width of 4.
set shiftwidth=4 " Indents will have a width of 4
set softtabstop=4 " Sets the number of columns for a TAB
set expandtab " Expand TABs to spaces
set list
set listchars=tab:>-
# first in .vimrc set up
:set expandtab
:set tabstop=4
# or you can do this
:set tabstop=4 shiftwidth=4 expandtab
# then in the py file in command mode, run
:retab!