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Python Navigation in Emacs

April 28th, 2017
python, code, tech  [html]

I'm now working full time in python in a medium-sized existing codebase, and I've started using jedi-mode for code navigation. What I really like about this package is that I can press C-c . to jump to the definition of something, and then C-c , to jump back again. What's especially cool about jedi is that it parses the python syntax tree, understands type hints, and can show you the definitions of things like attributes on arbitrary objects. Consider:

class Foo():
  def a():
    return 'foo'
class Bar():
  def a():
    return 'bar'
def baz(b: Foo) -> str:
  return b.a

In a simple tags or dumb-jump system there's no way to know that b.a is Foo.a and not Bar.a, but jedi-mode understands the python and jumps to the right place.

What I don't like about jedi-mode is that it also turns on other distracting things that get in the way of trying to write. If you hold the cursor still it pops up "quick help" that obscures the code below:

If you start to type something it recognizes it offers a completion, and if you press the wrong key you'll accidentally accept the completion:

And if you type something ambigous it can do both frustrating things at once:

I put up with this for a surprisingly long time before looking into fixing it, but these can be disabled. The key thing is that jedi-mode turns on auto-complete-mode, and it's auto-complete that's responsible for most of the behavior I don't like. So: here's how to turn on jedi in a non-instrusive way:

; move quick-help tooltips to the minibuffer
(setq jedi:tooltip-method nil)

; don't auto-complete unless requested
(setq ac-auto-start nil)
(setq ac-auto-show-menu nil)
(define-key ac-mode-map (kbd "M-TAB") 'auto-complete)

(add-hook 'python-mode-hook 'jedi:setup)

I'm pretty happy, but there are still two things I'd like:

  • C-c , on an empty stack should bring up a list of places a thing is used. That is, places where C-c . would bring you here.
  • Automated refactoring: rope has fallen way behind and can't handle python 3 codebases well. I'd love to be able to write "turn all calls to package.foo(...) into package._foo(...)" rules and have jedi automatically apply them.

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