I'm trying to find out if it's possible to make the write ":w" command perform a forced validation for certain file types.

My use case is that I want to prevent small typos and idention errors in python source code. So VIM should not even allow me to save a file with errors.

I can run "python -m py_compile filename" on a file to see if it compiles. This command returns nothing, if all is well, otherwise and error message like "Sorry: IndentationError: expected an indented block (hello.py, line 2)" Alas this requires me to save the file "filename, which I only want done if it passes.

So I'd need to automate these steps:

  • save the current file with a temporary filename, like filename.insert_uuid_here.py
  • run "python -m py_compile filename.insert_uuid_here.py

on success:

  • remove both the filename.insert_uuid_here.py and the __python_cache__/filename.insert_uuid_here.py file.

  • allow save

on fail:

  • remove the filename.insert_uuid_here.py

  • display error from compile attempt

Is this something, that's possible?

How could I link this to any ":w" attempt to write a python file?

  • 1
    Might be possible using a custom BufWriteCmd autocommand. I would however not recommend doing that. Commented Jun 9, 2018 at 9:26
  • It might be a better approach to allow writing while linting on save, but automate the checks to block at the build or deploy phase.
    – LEI
    Commented Jun 10, 2018 at 15:20
  • Does the python command follow basic shell command execution conventions? Specifically does it optionally allow input via stdin rather than a file and does it return 0 when input is clean and non-zero otherwise? If both of these are true I have a function for you.
    – B Layer
    Commented Jun 10, 2018 at 15:46

1 Answer 1


You can use ALE to asynchronously lint (i.e. check for style/syntax errors) while you type. This will not prevent vim from saving the buffer when you instruct it to do so but that might be what actually you need/want.

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