Document what exception should be raised when trying to open non-existent file

[Jonas H.]

What should custom storage backends raise if the file trying to open does not exist? (In Storage._open) That's not documented anywhere.

[Carl Meyer]

I can't find anywhere in Django that tries to catch an exception from calling .open() on a storage backend, and Django's FileSystemStorage doesn't catch the IOError and re-raise anything else, so at the moment I don't believe there is any such standard to document. For maximum compatibility with FileSystemStorage you'd want to raise IOError, I suppose.

I can see valid use cases (i.e. in reusable apps) for having some common exceptions standardized as part of the Storage interface, so accepting this as a feature request (not necessarily just for documentation, as FileSystemStorage should also use the common exception, and I'm not sure it should be IOError).

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Collin Anderson]

FileNotFoundError was added in Python 3.3 / PEP 3151 and kinda fixed this issue.

Could maybe help to document raising exceptions like FileNotFoundError here ​https://docs.djangoproject.com/en/dev/howto/custom-file-storage/ , though probably doesn't need to be super thoroughly documented, as it mostly should be similar to Python's open().

[Mariusz Felisiak]

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In 8edaf07a:

Fixed #15799 -- Doc'd that Storage._open() should raise FileNotFoundError when file doesn't exist.

[Mariusz Felisiak <felisiak.mariusz@…>]

In a22aeef5:

[4.2.x] Fixed #15799 -- Doc'd that Storage._open() should raise FileNotFoundError when file doesn't exist.

Backport of 8edaf07a28a3e3848ab1edbdcd2fdc25e6bd6015 from main