Stop vim from deleting expanded tab as a block of spaces

Question

I am on CentOS 8.1 and using vim 8.0.1763. When I open a python file, e.g. vim tmp.py, I type tab and it inserts 4 spaces (see .vimrc below). When I type delete, it deletes all 4 spaces. I want it to delete only one space. I'm pretty sure this was the case in vim 7.4.629. In vim 8.0.1763, it deletes only one space if it is a .txt file but 4 if it is a .py file.

.vimrc

set number
filetype plugin on  
syntax on
set paste
set formatoptions-=tc
set ruler
set showmatch
set expandtab
set tabstop=4

Question :

How do I get vim to only delete one space in python files? I assume this is set in /usr/share/vim/vim80/syntax/python.vi, but I'm not particularly familiar with the vim language.

Answer 1

What you're seeing is the result of having 'softtabstop' (alias 'sts') set to a non-zero value. It makes a lot of sense for this to be set in Python files where spacing matters since backspacing over individual spaces in indentation can lead to invalid Python.

If you really want to change it set 'sts' to 0. But you can't just put set sts=0 in your vimrc. It's being set well after your vimrc is sourced, i.e. after you load the file when the filetype (python) is identified.

There are a couple ways to set it but probably the most correct/appropriate is to put the setting in the file $VIMHOME/after/ftplugin/python.vim (where $VIMHOME is something like ~/.vim). You may have to create the file first.