Apply automatic pep8 fixes from QuickFix window

Background:

I'm using the (fantastic) Vim plugin python-mode, which includes the pep8 linter. The :PyLint command runs all linters and opens errors in a QuickFix window.

Problem:

Now, let's assume I'm only using the pep8 linter, and I have a QuickFix window full of errors. I'd like to step through each of these errors and apply an automatic fix (with something like autopep8). The autopep8 tool is fantastic, but it makes mistakes. Ideally, I'd like to be able to supervise each fix in Vim (apply fix, check, move to next fix).

My current approach is to run autopep8 on my Python file, diff the results, then repair any bad changes:

$ autopep8 --in-place spam.py
$ git difftool spam.py  # check edits in gVim, write to file
$ git commit spam.py -m "Fix bad PEP8 formatting"

However, this approach ruins my undo history, and seems needlessly complex. Is there a better way?

Question:

Is there any way to automatically apply pep8 fixes (when available) to pep8 errors within the QuickFix window?

Solution

Options

There are two simple answers that won't wipe out your undo history.

1. Diff with the saved file in Vim

I found this DiffWithSaved function online quite a while ago and it has been very useful. In this case, you can just run autopep8 in the terminal, and when Gvim asks to reload the file, choose no and then run this function, which will pop up a scratch buffer with your new file and allow you to change things around.

" copy this to your vimrc or source it

" tells vim not to automatically reload changed files
set noautoread 

function! DiffWithSaved()
  let filetype=&ft
  diffthis
  vnew | r # | normal! 1Gdd
  diffthis
  exe "setlocal bt=nofile bh=wipe nobl noswf ro ft=" . filetype
endfunction

" sets up mappings to function

com! DiffSaved call DiffWithSaved()
map <Leader>ds :DiffSaved<CR>

Once you run that, you can use the vim copy-diff and other diff commands to quickly go through and accept/not accept changes. Plus, all will be stored in undo history.

" run these commands after sourcing the above function

" % expands to filename (also %:h to head, %:t to tail)
" if it throws an error, just do :cd %:h first

:!autopep8 --in-place %
:DiffSaved

2. Diff with the git `difftool` and reload the file

If you want to diff with the file in the git index (and using git's difftool), you could do the following:

leave gvim open,
run your commands in the terminal and let the program open up a new instance of gvim (or vim) to handle the diffing.
Save it all.
Go back to your original gvim, let vim reload the file and (at least to my knowledge) your undo history should remain.

Advantages/Disadvantages

Option 1

Advantages:

each change will be saved in your undo history
graphical diffs in vim are easy to read

Disadvantages:

Won't be using git's difftool
relies upon vim's diff functions.

Option 2