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pythonflaskmemoizationflask-cache

flask_cache and memoize - make_cache_key error: object of type 'NoneType' has no len()

I'm kind of new to using flask, and I want to cache the result of a function that reads pickled data. I use memoize function from flask_cache as follows:

in model_chacher.py:

from flask_cache import Cache
import pickle


model_cache = Cache(config={'CACHE_TYPE': 'simple'})


class ModelCacher():
    @model_cache.memoize(50)
    def get_model(self, customer_ID):

        with open('/path/to/data.pickle', 'rb') as tf:
            model_args = pickle.load(tf)
            trained_classifier = model_args[0]

        return trained_classifier

in flask_compose.py:

from flask import Flask
from controllers.topic import controller as topic_controller
from models.modelcache.model_chacher import model_cache


app = Flask(__name__)
model_cache.init_app(app)
app.register_blueprint(topic_controller.topic_controller_blueprint)


if __name__ == '__main__':
    app.run(host="0.0.0.0", port=80, debug=True)

and I call ModelCacher.get_model(customer_ID) in topic_controller:

from models.modelcache.model_chacher import ModelCacher
...
trained_classifier = ModelCacher.get_model(cls_str)
...

and after running flask_compose.py and sending a request I get the following result:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1997, in __call__
    return self.wsgi_app(environ, start_response)
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1985, in wsgi_app
    response = self.handle_exception(e)
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1540, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python3.6/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1982, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1614, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1517, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python3.6/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1612, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1598, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/app/controllers/topic/controller.py", line 20, in classify
    return ModelCacher.get_model(cls_str)
  File "/usr/local/lib/python3.6/site-packages/flask_cache/__init__.py", line 528, in decorated_function
    cache_key = decorated_function.make_cache_key(f, *args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/flask_cache/__init__.py", line 393, in make_cache_key
    **kwargs)
  File "/usr/local/lib/python3.6/site-packages/flask_cache/__init__.py", line 434, in _memoize_kwargs_to_args
    elif abs(i-args_len) <= len(argspec.defaults):
TypeError: object of type 'NoneType' has no len()

and my question is: how to properly set up my cache? any help is greatly appreciated.

EDIT: WHAT SOLVED MY PROBLEM:

as @stamaimer pointed out, I create and instance of my ModelCacher and that solved the problem, also I used cached from flask_cache.Cache instead of memoize.

Solution

  • The get_model method your defined is a instance method instead of a class method. You use ModelCacher.get_model(cls_str) when call the method. Try to call it with ModelCacher().get_model(cls_str). Or you can just defined it as a global function.