Improve error handling for SpacyPreprocessor without model

[bhancock8]

Is your feature request related to a problem? Please describe.

The first time a user tries to use the SpacyPreprocessor, they hit they following error:

  File "<stdin>", line 1, in <module>
  File "/Users/braden/anaconda3/lib/python3.7/site-packages/spacy/__init__.py", line 27, in load
    return util.load_model(name, **overrides)
  File "/Users/braden/anaconda3/lib/python3.7/site-packages/spacy/util.py", line 139, in load_model
    raise IOError(Errors.E050.format(name=name))
OSError: [E050] Can't find model 'en_core_web_sm'. It doesn't seem to be a shortcut link, a Python package or a valid path to a data directory.

Describe the solution you'd like

We know the line where the spacy model is called (

snorkel/snorkel/preprocess/nlp.py

Line 62 in 9af1c77

self._nlp = spacy.load(language, disable=disable or [])

) and should be able to catch that Exception and download it if its missing.

[henryre]

Agreed! Let's just raise a more informative error rather than downloading something possibly unexpected.

[rjurney]

@henryre @bhancock8 I have a related problem instantiating SpacyPreprocessor here: #1496

[rjurney]

I’m going to fix this over the weekend.