Why is my Python indentation set to 8 locally by default?

Question

I'm running Emacs 25.2.2 on Ubuntu 18.04 for WSL. I launch emacs -q and open a new Python file, test.py. As soon as I hit the Tab key, I notice the indentation is 8 spaces instead of 4. I don't like that.

I run describe-variable to check on python-indent and I see:

python-indent is a variable defined in ‘python.el’.
Its value is 8
Local in buffer test.py; global value is 4

    This variable is an alias for ‘python-indent-offset’.   
    This variable is obsolete since 24.3; 
    use ‘python-indent-offset’ instead.`

[...]

As for the preferred variable:

python-indent-offset is a variable defined in ‘python.el’.
Its value is 4

[...]

Am I correct to think that this is a major bug in the default Python mode? What's the simplest fix or workaround?

Answer 1

The default is 4 spaces:

(defcustom python-indent-offset 4
  "Default indentation offset for Python."
  ...

But python-mode guesses the spaces when opening a file and overwrites the default locally. That's probably what happens in your case as only the local value is set to 8 and the global (default) is still 4.

Try it with a new empty file and check the value of the variable again.

You can also disable this feature:

(setq python-indent-guess-indent-offset nil) ; default is t

Answer 2

I cannot reproduce this using "emacs-24.2 -q ", where the default is correct at the value 4. I suggest you update your emacs, or perhaps there is something odd about your file test.py if it is an already existing python file.