Python Flask app runs locally, but returns AttributeError when hosted on Heroku

I would try putting

clf = joblib.load('ENS_fitted.joblib')

into a try-except block to see if the exception there is the same as what you're getting at

AttributeError: module '__main__' has no attribute 'FlexibleScaler'

For Example:

try:    clf = joblib.load('ENS_fitted.joblib')    prediction = clf.predict(features)    pred_prob = clf.predict_proba(features)except Exception as e:    print(f"Exception: {e}")

Also, I recommend making sure that gunicorn is calling the program as name == "main" by printing out a notice to yourself;

if __name__ == "__main__":    print("__name__ is __main__")    app.run(debug = True)

If you can't get past the error after doing this, I would look into configuring gunicorn with flask.

It appears that the joblib.save() that produced ENS_fitted.joblib happened in flask_start.py was run directly from python. When that's the case, flask_start will have a __name__ of "__main__". Then, when joblib.save() pickles, it will save the FlexibleScaler instance as a __main__.FlexibleScaler.

But when you deploy and run under gunicorn, flask_start will have a __name__ of "flask_start". This confounds joblib.load(), which expects to find a __main__.FlexibleScaler, and gives up as you've shown above.

A solution to this is to regenerate your saved model, but this time by invoking flask_start via

% FLASK_APP=flask_start flask run

then joblib.save() again, then re-deploy.

Updated

If you're absolutely unable to get the model regenerated, you can try this hack. After the imports in flask_start.py, add

import __main____main__.FlexibleScalar = FlexibleScalar

You'll either be able to joblib.load() the model, or you'll run into a similar error with another class, in which case, repeat this trick.