CODEWITHSUNDEEP
emacshookelisp
Hanfei Sun
Hanfei Sun

Reputation: 47051

When will the functions held by a hook be run in emacs?

For example, I put some codes within python-mode-hook, and the codes will be run when:

(1) Every time I open a python file *.py

(2) Only the first time that python-mode was triggered

Does anyone have ideas that which answer is right?

Thanks!

Upvotes: 3

Views: 217

Answers (3)

phils
phils

Reputation: 73274

If you want to look at the code, then note that the vast majority of major modes are constructed with the define-derived-mode macro (modes can simply supply nil for the parent if the new mode does not actually derive from another one, in order to still get the same benefits and standard behaviours from using the macro).

So M-x find-function RET define-derived-mode RET

You'll see that the very last thing that happens when the mode is invoked is (run-mode-hooks ',hook) (where ,hook in this instance will expand to the name of the mode with a -hook suffix).

So every time a buffer enables that mode (meaning that the mode function defined by that macro is executed), the mode's hook is also run (as well the hooks for any parent/ancestor modes -- the interesting delay-mode-hooks and run-mode-hooks interaction means that none of the hooks are run until all the other processing has been completed).

Upvotes: 4

Dale Hagglund
Dale Hagglund

Reputation: 16440

There is no general rule about when hooks run: this is controlled solely by the code which defines the hook. However, there are general conventions that are followed among which is this one:

  • If foo-mode is a major mode of some sort, then foo-mode-hook will run each time foo-mode is enabled in a buffer.

In particular, as has already been pointed out, the functions in python-mode-hook run every time a .py file is loaded.

Upvotes: 6

Oleg Pavliv
Oleg Pavliv

Reputation: 21172

It will run every time you open a python file.

Then python mode will be triggered for this file buffer and your hook will be executed.

You can easily test this by writing a simple hook:

(add-hook 'python-mode-hook  (lambda () (message "python mode hook")))

Upvotes: 3

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