Dash app suddenly fails

Everything has been running fine for weeks, but this morning I couldn't load the dash app.  WeatherStem is still updating just fine.
Here's the error I get when trying to run the index.py script as sudo, without the &.  


Traceback (most recent call last):
 File "index.py", line 5, in <module>
   import dash_core_components as dcc
 File "/usr/local/lib/python3.7/dist-packages/dash_core_components/__init__.py", line 22, in <module>
   from ._imports_ import *  # noqa: F401, F403, E402
 File "/usr/local/lib/python3.7/dist-packages/dash_core_components/_imports_.py", line 9, in <module>
   from .Interval import Interval
 File "<frozen importlib._bootstrap>", line 983, in _find_and_load
 File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
 File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
 File "<frozen importlib._bootstrap_external>", line 724, in exec_module
 File "<frozen importlib._bootstrap_external>", line 857, in get_code
 File "<frozen importlib._bootstrap_external>", line 525, in _compile_bytecode
ValueError: bad marshal data (unknown type code)

Nothing had changed.  I just checked the dash info one morning, and it couldn't connect.  
Any hints?