Update Werkzeug and add pyyaml

[wbrgss]

When running npm run build in this repo, within a virtual environment:

• Without upgrading Werkzeug to 0.15.6 I got

  from .wrappers import Request
  File "/home/plotly/Workspace/dash-table/ve/lib/python3.7/site-packages/flask/wrappers.py", line 14, in <module>
  from werkzeug.wrappers.json import JSONMixin as _JSONMixin
ModuleNotFoundError: No module named 'werkzeug.wrappers.json'; 'werkzeug.wrappers' is not a package

Maybe we could also use a different version of Flask. In the end it might be a Flask bug (see here)

• Without installing pyyaml from pip:

Traceback (most recent call last):
  File "/home/plotly/Workspace/dash-table/ve/bin/dash-generate-components", line 5, in <module>
    from dash.development.component_generator import cli
  File "/home/plotly/Workspace/dash-table/ve/lib/python3.7/site-packages/dash/development/component_generator.py", line 14, in <module>
    import yaml
ModuleNotFoundError: No module named 'yaml'

I'm using PopOS (a flavour of Ubuntu 19.04). @Marc-Andre-Rivet can you check if bumping the Werkzeug version breaks anything in your env and/or whether pyyaml is already in your env?

[wbrgss]

Not sure what happened here; whitespace strip?

[alexcjohnson]

Your editor probably added a trailing newline, which @Marc-Andre-Rivet's files often don't have. No worries, I do that all the time too 😏

[alexcjohnson]

@Marc-Andre-Rivet What is this requirements.txt file? The only place I see it mentioned is in the "local server review apps" section of CONTRIBUTING.md. For running npm run build I'd think you want to be in an environment that has dash[dev] installed, and that'll bring along PyYAML with it (and then after that reinstall the table repo -e).

Re: Werkzeug - I guess that should have been updated with Flask in #536, but I don't know why this requirements.txt file is locking down things we don't depend on directly, that seems like a recipe for all sorts of problems, unless this file is autogenerated from some other clean install process

[Marc-Andre-Rivet]

@alexcjohnson I think this file is used for the Heroku deployment from GH:

Not sure if dev-requirements and python-requirements have any use at this point though.

[shammamah-zz]

@wbrgss pyyaml should be installed automatically with pip install dash[dev]. We might have to update the contributing guidelines instead to specify that that package should be installed.

[Marc-Andre-Rivet]

Removing the pyyaml entry. As @shammamah pointed out this is included with dash[dev].