ALLOWED_HOSTS no longer accepts a non-list/tuple iterable.

[Carlton Gibson]

cdd0b213a825fcfe90ae93dcc554fba8c1e5ff5d added ALLOWED_HOSTS to the list of tuple_settings that are checked to be lists or tuples in Settings.__init__().

This causes a regression with settings such as:

class AllowedHosts:
    """
    An allowed hosts proxy, implementing SOME logic to determine ALLOWED_HOSTS.
    """

    DEBUG_ALLOWED_HOSTS = ["localhost", "127.0.0.1", "[::1]"]

    def __iter__(self):
        if settings.DEBUG:
            yield from self.DEBUG_ALLOWED_HOSTS

        yield "domain.com"
        yield "domain.org"
        yield from [
            "other-domain.com",
            "www.other-domain.com",                                                                                         
        ]
        
ALLOWED_HOSTS = AllowedHosts()

This works fine before Django 4.0 but raises afterwards:

raise ImproperlyConfigured("The %s setting must be a list or a tuple." % setting)
django.core.exceptions.ImproperlyConfigured: The ALLOWED_HOSTS setting must be a list or a tuple.

We could revert cdd0b213a825fcfe90ae93dcc554fba8c1e5ff5d, or else adjust the test. I think the force of it is "iterable() but not a string"? 🤔

[Mariusz Felisiak]

It's ​documented that ALLOWED_HOSTS is "a list of strings representing...", it was also discussed in one of ​PRs. I wouldn't consider it as a regression, sorry :) I'm of course open to discussion.

[Carlton Gibson]

OK, we can say that 😜
(It’s worked this way since ≈forever, so it is a change in behaviour, but there’ll be another way.)

[Adam Johnson]

There's nothing complicated about your class there, it can be determined at import time right? It only depends on whether DEBUG is True or not.

You could always make your setting a subclass of list and override __iter__ if really required.

[Carlton Gibson]

The example is simplified, but I can work around, yes. I do feel we've cut out a legitimate use-case with an overly strict test — it demands more than we need — but it's not something I want to spend time pushing on now. (Not a problem!)

[Claude Paroz]

I agree with Carlton, those checks are not totally Pythonic (duck typing and all...) and could probably be improved.