TypeError: object of type 'MeanField' has no len() during pm.sample_posterior_predictive

[junpenglao]

Object returns from pm.fit is not a MultiTrace like object, you should do something like:

mean_field = pm.fit(...)
trace = mean_field.sample(500)

For more see:
https://docs.pymc.io/notebooks/variational_api_quickstart.html