import ipywidgets fails under -OO

[mattpap]

This can be reproduced on master with:

$ python -OO -c "import ipywidgets; print(ipywidgets.__version__)"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "ipywidgets/ipywidgets/__init__.py", line 25, in <module>
    from .widgets import *
  File "ipywidgets/ipywidgets/widgets/__init__.py", line 13, in <module>
    from .widget_box import Box, HBox, VBox, GridBox
  File "ipywidgets/ipywidgets/widgets/widget_box.py", line 33, in <module>
    class Box(DOMWidget, CoreWidget):
  File "ipywidgets/ipywidgets/widgets/docutils.py", line 11, in decorator
    cls.__doc__ = cls.__doc__.format(**stripped_snippets)
AttributeError: 'NoneType' object has no attribute 'format'

After adding a check for None in ipywidgets.widgets.docutils, the correct behavior is restored:

$ python -OO -c "import ipywidgets; print(ipywidgets.__version__)"
7.5.1

[jasongrout]

Looks like -OO discards docstrings:

-OO    : do -O changes and also discard docstrings; add .opt-2 before
         .pyc extension

So apparently we should not assume the __doc__ attribute exists, or at least we should not assume it is a string.

[jasongrout]

After adding a check for None in ipywidgets.widgets.docutils, the correct behavior is restored:

Can you submit a PR?

[mattpap]

@jasongrout, see PR #2525.