Opened 4 years ago

Last modified 12 months ago

#27747 new New feature

Add signals for Django management commands

Reported by: Dmitry Gladkov Owned by: nobody
Component: Core (Management commands) Version: master
Severity: Normal Keywords:
Cc: Triage Stage: Someday/Maybe
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no


Related PR:

Suggested example usage (I know that a string can't be a signal sender, this is just for illustrating the point):

from import signals

def handle_pre(sender, instance):
    instance.stdout.write('Hello World')

def handle_post(sender, instance):
    instance.stdout.write('Bye World')

signals.pre_command.connect(handle_pre, sender='runserver')
signals.post_command.connect(handle_post, sender='runsever')


Currently overriding of commands in Django can only be achieved by shadowing existing commands using INSTALLED_APPS initialization order. This is a perfectly good solution if a user needs to completely override a command, but it's not ideal for extending/adding functionality to existing commands. Extending the same command from different apps will not work as only the extended command from the latest INSTALLED_APPS entry will run (see Example 2).

Some examples of actions that can be achieved using singals:

  1. Pulling remote translations before compilemessages.
  2. Showing coverage or/and generating xml report after test.
  3. Running optipng on collected static images after collectstatic
  4. Displaying useful information like outdated package versions before runserver.

Change History (3)

comment:1 Changed 4 years ago by Tim Graham

Triage Stage: UnreviewedSomeday/Maybe

I'd like to see a consensus on the DevelopersMailingList before accepting this feature. Adam already offered an opinion, "If there are other use cases I think they'd also normally be better handled by more specific signals, e.g. post_migrate, rather than a generic all-commands signal." but this should be proposed on a separate thread.

comment:2 Changed 12 months ago by Matthew Schinckel

The one I have in mind is being able to fire off a seperate process when starting runserver (for instance, to make sure that our JS build pathway stuff has a "watch" server running).

comment:3 Changed 12 months ago by Carlton Gibson

For runserver, in particular, I'm suspecting that, at this late stage, they'll be some kind of rewrite making it async, to use presumably asyncio. The autoreloader in the particular seems to be crying out for this... As such, I'd suggesting adding functionality as part of that to control subprocesses (or whatever else) rather than using signals.

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