Consolidate the file upload widget value metadata and content?

[jasongrout]

We've recently discussed the format for the file upload value attribute. It looks like what was settled on was something like:

[{'metadata': {'name': 'Untitled1.ipynb',
   'type': '',
   'size': 1734,
   'lastModified': 1552316652863},
  'content': <memory at 0x10eeadd00>}]

In playing around with it a bit, it seems much simpler to just combine it into one dictionary, sort of like how the Jupyter contents api does it:

[{'name': 'Untitled1.ipynb',
   'type': '',
   'size': 1734,
   'lastModified': 1552316652863,
   'content': <memory at 0x10eeadd00>}]

I think it's simpler to not have to go through the metadata key, like:

for f in widget.value:
    print(f['name'])
    print(f['size'])
    print(f["content"].tobytes().decode("utf-8"))

Thoughts?

[pbugnion]

I agree having a single top-level dictionary is simpler. I think this was just forgotten about when we pushed #2666.

[jasongrout]

Also, I notice in the documentation from #2714, we have an example of converting the contents to a string: uploaded_file["content"].tobytes().decode("utf-8"). As far as I can tell, this creates an extra copy (tobytes does a copy). It would probably be better to do:

import codecs
codec.decode(uploaded_file["content"], 'utf-8')

which does not do an extra copy by working on the memory view directly.

[pbugnion]

Ah I hadn't realised that difference between .tobytes and using codecs. Thanks!

I've addressed the docs issue in #2722.

[jtpio]

Agree a single dict is simpler.

PR incoming.

[pbugnion]

Fixed by #2724 and #2722.