This exception is used during development to indicate that in that place you need to implement some functionality. For example method in a subclass.
Let's define a parent class:
class Animal(object): def __init__(self, speed): self.speed = speed def run(self): raise NotImplementedError('You need to implement this method in %s.' % self.__class__.__name__)
And some child class which will inherit all methods:
class Rabbit(Animal): pass
Now let's try to create a class instance and run a method from the parent class:
rabbit = Rabbit(speed=20) rabbit.run()
in run raise NotImplementedError(NotImplementedError: You need to implement this method in Rabbit.)
So it says that you are using a method that actually is not implemented, so most likely you have to implement it in Rabbit class.