When and why to use raise NotImplementedError in Python?

General Discussions
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#1

When should you use raise NotImplementedError in Python?

Is it primarily to remind yourself or your team to implement the methods in a class properly? I’m struggling to fully understand the use of an abstract class with this pattern:

class RectangularRoom(object):
    def __init__(self, width, height):
        raise NotImplementedError

    def cleanTileAtPosition(self, pos):
        raise NotImplementedError

    def isTileCleaned(self, m, n):
        raise NotImplementedError

Could you clarify how python NotImplementedError fits in this context?

#2

Hey @sndhu.rani

Here is the question to your answer:-

Using python notimplementederror for Abstract Methods in Non-Abstract Classes Raising NotImplementedError is a common way to indicate that methods are meant to be overridden in subclasses. While Python doesn’t enforce abstract methods in regular classes, this approach acts as a clear signal for developers.

For example, in the RectangularRoom class:

class RectangularRoom:  
    def cleanTileAtPosition(self, pos):  
        raise NotImplementedError("Subclasses must implement this method.")

Here, python notimplementederror ensures that if a subclass does not implement the cleanTileAtPosition method, an exception is raised, preventing incorrect usage of the class.

#3

Hello Everyone,

Improving Abstract Method Definition with ABCs Instead of python notimplementederror

While manually using python notimplementederror works, Python offers a cleaner and more enforceable solution through Abstract Base Classes (ABCs) in the abc module.

Refactoring the previous example with ABC and @abstractmethod:

from abc import ABC, abstractmethod  

class RectangularRoom(ABC):  
    @abstractmethod  
    def cleanTileAtPosition(self, pos):  
        pass  

    @abstractmethod  
    def isTileCleaned(self, m, n):  
        pass

This approach ensures that any attempt to instantiate RectangularRoom or its subclasses without implementing the abstract methods raises an error at runtime, offering stricter control compared to python notimplementederror.

Let me know if you have further doubts.

#4

Hey All!

Using python notimplementederror as a Development Placeholder

In addition to indicating abstract methods, python notimplementederror is useful during the development phase when a method’s logic isn’t ready yet. It acts as a placeholder to ensure the method isn’t unintentionally used.

For example:

class RectangularRoom:  
    def cleanTileAtPosition(self, pos):  
        # TODO: Implement this method later  
        raise NotImplementedError("cleanTileAtPosition is not yet implemented.")  

    def isTileCleaned(self, m, n):  
        # TODO: Add logic here  
        raise NotImplementedError("isTileCleaned is not yet implemented.")

Using python notimplementederror here ensures that partially implemented methods don’t make it to production while signaling to other developers (or yourself) that these need further work. It’s a handy reminder in agile workflows.