`new_untitled` has fixed notebook extension

[stevenmanton]

I'm working on creating a custom FileContentsManager to work with gpg-encrypted notebooks and ran into a minor issue. One thing I'd like to do is work with notebooks that have the extension .ipynb.gpg. However, the .ipynb is hard-coded in the ContentsManager class. It seems unnecessary. Could we change that from ext = '.ipynb' to ext = ext or '.ipynb' to allow for overloading?

[Carreau]

Hum. @ellisonbg , @blink1073 , @jasongrout is that possible with the new jupyter-js-services ?

[blink1073]

jupyter-js-services is agnostic to file extension, this requires a change to the server.

[minrk]

We can make notebook extension a (non-configurable) attribute on the ContentsManager, and then custom ContentsManagers can use a different extension.

[stevenmanton]

Thanks for the suggestion @minrk. Would you be restricted to just one nb extension then? My implementation reads regular .ipynb notebooks regularly, but passes notebooks ending in .ipynb.gpg through decryption/encryption when reading/writing. So in a sense it works with multiple nb extensions.

It was actually quite easy to implement this, thanks to the well thought out API. I only had to extend the FileManagerMixin class methods open and atomic_writing, and the FileContentsManager methods new_untitled and increment_filename. I filed this issue because I had to copy the code of new_untitled into my subclass and modify one line because it won't let me override the extension.

[minrk]

@stevenmanton for new_untitled, it's probably going to be a single value because there's no mechanism to pick between choices. For the most part, the contents API shouldn't be sensitive to notebook extensions, as it's up to the CM implementation to determine whether a file is a notebook or not.

[stevenmanton]

I guess what I had in mind was that if the line I mentioned above was ext = ext or '.ipynb' then when I override the new_untitled method I could just do something like following, rather than copying the entire contents of new_untitled, if that makes sense.

def new_untitled(self, path='', type='', ext=''):
    if type == 'notebook' and not ext:
        ext = '.ipynb.gpg'
    return super().new_untitled(path=path, type=type, ext=ext)

[AbdealiLoKo]

Setting the ext makes sense IMO. It would not break anything either and is useful for ContentsManager creators.
If this is an OK solution, let me know, I'll make a pull request