Context manager clarification

[asdf-format]

Context manager clarification

[mdboom]

This is somewhat historical (when you create an AsdfFile, it may not have an underlying file object and therefore there is nothing to close). It should probably just be cleaned up in the docs/tests and elsewhere.

Actually, this use case is definitely valid, and in some cases the best way to "spell" things. First, when you make a raw AsdfFile, it has no on-disk file associated with it. Secondly, if you want to write the same AsdfFile to multiple files, you'll want a context manager around each call to write_to. Third, we can't just have write_to close the file because the user may want to keep the file open for updating (or accessing mem-mapped content).

An alternative could be to have other methods or keyword arguments that indicate "keep open for later updating"...

I guess the source of the confusion here is that AsdfFile objects aren't necessarily always associated with a file on disk? There's good reasons to want to do that -- validation without using the disk or a StringIO, for example.

#116 is a possible solution to this, but I'd also consider code changes that still keep updating possible...