'collectstatic' management command inappropriately eating AttributeError exceptions

[Brett G]

Recently, Django 5.0 ​removed the django.utils.timezone.utc alias to datetime.timezone.utc.

I've written a custom file storage class that implements a get_modified_time method which, predictably, used the django.utils.timezone.utc alias.

The code in 'django/contrib/staticfiles/management/commands/collectstatic.py' reads as follows:

            try:
                # When was the target file modified last time?
                target_last_modified = self.storage.get_modified_time(prefixed_path)
            except (OSError, NotImplementedError, AttributeError):
                # The storage doesn't support get_modified_time() or failed
                pass
            else:
                try:
                    # When was the source file modified last time?
                    source_last_modified = source_storage.get_modified_time(path)
                except (OSError, NotImplementedError, AttributeError):
                    pass

I assume the exception catch there is meant to ignore AttributeError exceptions from custom file storage classes that do not implement get_modified_time. This is inappropriate - custom file storage classes can be written by users, and the get_modified_time method may raise AttributeError for a completely unrelated reason.

The net effect of this is that when collectstatic was run, all static files were copied, regardless of modification time, as collectstatic silently ignored this error. This was difficult to pin down.

Checking for the presence of a get_modified_time attribute using duck typing (eg. hasattr(self.storage, 'get_modified_time')) may be more appropriate than eating such a generic exception.