How do I implement interfaces in python?

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public interface IInterface
{
    void show();
}

 public class MyClass : IInterface
{

    #region IInterface Members

    public void show()
    {
        Console.WriteLine("Hello World!");
    }

    #endregion
}

How do I implement Python equivalent of this C# code ?

class IInterface(object):
    def __init__(self):
        pass

    def show(self):
        raise Exception("NotImplementedException")


class MyClass(IInterface):
   def __init__(self):
       IInterface.__init__(self)

   def show(self):
       print 'Hello World!'

Is this a good idea?? Please give examples in your answers.

As mentioned by other here:

Interfaces are not necessary in Python. This is because Python has proper multiple inheritance, and also ducktyping, which means that the places where you must have interfaces in Java, you don't have to have them in Python.

That said, there are still several uses for interfaces. Some of them are covered by Pythons Abstract Base Classes, introduced in Python 2.6. They are useful, if you want to make base classes that cannot be instantiated, but provide a specific interface or part of an implementation.

Another usage is if you somehow want to specify that an object implements a specific interface, and you can use ABC's for that too by subclassing from them. Another way is zope.interface, a module that is a part of the Zope Component Architecture, a really awesomely cool component framework. Here you don't subclass from the interfaces, but instead mark classes (or even instances) as implementing an interface. This can also be used to look up components from a component registry. Supercool!

Does Python supports interfaces like in Java or C#?, The access specifiers used with classes are private, protected and public. Interfaces are not necessary in Python. This is because Python has proper multiple inheritance, and also ducktyping, which means that the places where you must have interfaces in Java, you don't have to have them in Python. That said, there are still several uses for interfaces.

Using the abc module for abstract base classes seems to do the trick.

from abc import ABCMeta, abstractmethod

class IInterface:
    __metaclass__ = ABCMeta

    @classmethod
    def version(self): return "1.0"
    @abstractmethod
    def show(self): raise NotImplementedError

class MyServer(IInterface):
    def show(self):
        print 'Hello, World 2!'

class MyBadServer(object):
    def show(self):
        print 'Damn you, world!'


class MyClient(object):

    def __init__(self, server):
        if not isinstance(server, IInterface): raise Exception('Bad interface')
        if not IInterface.version() == '1.0': raise Exception('Bad revision')

        self._server = server


    def client_show(self):
        self._server.show()


# This call will fail with an exception
try:
    x = MyClient(MyBadServer)
except Exception as exc:
    print 'Failed as it should!'

# This will pass with glory
MyClient(MyServer()).client_show()

What is Interface in Java with Example, are a mechanism for labeling objects as conforming to a given API or contract. So, this package can be considered as implementation of the Design By Contract methodology support in Python. Python provides many different ways to satisfy a simple function interface, and you can choose the one that works best for what you need to accomplish. Things to Remember # Instead of defining and instantiating classes, you can often simply use functions for simple interfaces between components in Python.

interface supports Python 2.7 and Python 3.4+.

To install interface you have to

pip install python-interface

Example Code:

from interface import implements, Interface

class MyInterface(Interface):

    def method1(self, x):
        pass

    def method2(self, x, y):
        pass


class MyClass(implements(MyInterface)):

    def method1(self, x):
        return x * 2

    def method2(self, x, y):
        return x + y

zope.interface · PyPI, 's defined members is considered to be a subclass of it for purposes of static type analysis. In Python, there is no need for interfaces. This is because Python has proper multiple inheritances, and also duck typing, which means that the places where you must have interfaces in Java, you don't have to have them in Python.

There are third-party implementations of interfaces for Python (most popular is Zope's, also used in Twisted), but more commonly Python coders prefer to use the richer concept known as an "Abstract Base Class" (ABC), which combines an interface with the possibility of having some implementation aspects there too. ABCs are particularly well supported in Python 2.6 and later, see the PEP, but even in earlier versions of Python they're normally seen as "the way to go" -- just define a class some of whose methods raise NotImplementedError so that subclasses will be on notice that they'd better override those methods!-)

What to use in replacement of an interface/protocol in python, In this post, we will explore how interfaces can be implemented in Python. Informal Interfaces: Protocols / Duck Typing. There's no interface  Interfaces in Python: Protocols and ABCs. Python. The idea of interface is really simple - it is the description of how an object behaves. An interface tells us what an object can do to play it’s role in a system. In object oriented programming, an interface is a set of publicly accessible methods on an object which can be used by other parts of the program to interact with that object.

Implementing interfaces with abstract base classes is much simpler in modern Python 3 and they serve a purpose as an interface contract for plug-in extensions.

Create the interface/abstract base class:

from abc import ABC, abstractmethod

class AccountingSystem(ABC):

    @abstractmethod
    def create_purchase_invoice(self, purchase):
        pass

    @abstractmethod
    def create_sale_invoice(self, sale):
        log.debug('Creating sale invoice', sale)

Create a normal subclass and override all abstract methods:

class GizmoAccountingSystem(AccountingSystem):

    def create_purchase_invoice(self, purchase):
        submit_to_gizmo_purchase_service(purchase)

    def create_sale_invoice(self, sale):
        super().create_sale_invoice(sale)
        submit_to_gizmo_sale_service(sale)

You can optionally have common implementation in the abstract methods as in create_sale_invoice(), calling it with super() explicitly in the subclass as above.

Instantiation of a subclass that does not implement all the abstract methods fails:

class IncompleteAccountingSystem(AccountingSystem):
    pass

>>> accounting = IncompleteAccountingSystem()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Can't instantiate abstract class IncompleteAccountingSystem with abstract methods
create_purchase_invoice, create_sale_invoice

You can also have abstract properties, static and class methods by combining corresponding annotations with @abstractmethod.

Abstract base classes are great for implementing plugin-based systems. All imported subclasses of a class are accessible via __subclasses__(), so if you load all classes from a plugin directory with importlib.import_module() and if they subclass the base class, you have direct access to them via __subclasses__() and you can be sure that the interface contract is enforced for all of them during instantiation.

Here's the plugin loading implementation for the AccountingSystem example above:

...
from importlib import import_module

class AccountingSystem(ABC):

    ...
    _instance = None

    @classmethod
    def instance(cls):
        if not cls._instance:
            module_name = settings.ACCOUNTING_SYSTEM_MODULE_NAME
            import_module(module_name)
            subclasses = cls.__subclasses__()
            if len(subclasses) > 1:
                raise InvalidAccountingSystemError('More than one '
                        f'accounting module: {subclasses}')
            if not subclasses or module_name not in str(subclasses[0]):
                raise InvalidAccountingSystemError('Accounting module '
                        f'{module_name} does not exist or does not '
                        'subclass AccountingSystem')
            cls._instance = subclasses[0]()
        return cls._instance

Then you can access the accounting system plugin object through the AccountingSystem class:

>>> accountingsystem = AccountingSystem.instance()

(Inspired by this PyMOTW-3 post.)

Implementing an interface is a way of writing an organized code and achieve abstraction. The package zope.interface provides an implementation of “object  Interfaces are not necessary in Python. This is because Python has proper multiple inheritance, and also ducktyping, which means that the places where you musthave interfaces in Java, you don't have to have them in Python. That said, there are still several uses for interfaces. Some of them are covered by Pythons Abstract Base Classes, introduced in Python 2.6.

How to implement an interface in Python. class AbstractClass(abc. ABC): def method(self): Subclasses must implement `method` class SubClass(AbstractClass): def method(self): Subclass implements `method` print("subclass method called") a_sub_class = SubClass() a_sub_class. method() So if you ever need to introduce an interface in Python3, I highly suggest you use annotations to describe the types of your arguments. Future you and users of your interface will thank you for this. One last word. They are tools like mypy that go even further and use annotations to provide gradual static typing for Python.

Functionally, abstract base classes let you define a class with abstract methods, which all subclasses must implement in order to be initialized. ABCs are extremely  implement interface X, I can pass them all as parameters to functions or whatnot that require an X object. Is there something similar in Python? What I'd like to do is create a feature detection system for my work-- specifically, a general class / interface called "Feature" and then subclasses that implement functions like isFeaturePresent() in

Zope's Interface package is used as the reference implementation for this There are many implied interfaces in Python, commonly referred to  In addition, any code that uses the keyword interface as an identifier will be issued a warning from Python. After the appropriate period of time, the interface syntax would become standard, the above import statement would do nothing, and any identifiers named interface would raise an exception.

Comments
  • What would be the purpose for using an interface in your case?
  • Frankly no purpose at all ! I just want to learn what to do when you need interfaces in python?
  • raise NotImplementedError is what show's body should be -- makes no sense to raise a completely generic Exception when Python defines a perfectly specific built-in one!-)
  • Shouldn't init call show() in IInterface (or raise the exception itself) so you can't instantiate an abstract interface?
  • I can see some use for this... let's say you have an object that you want to ensure has a specific signature. With duck typing you can't guarantee that the object will be of the signature that you expect. Sometimes it might be useful to enforce some typing on dynamically typed properties.
  • Could you elaborate on this? 1. How does one implement such an interface? 2. How can it be used to look up components?
  • "Interfaces are not necessary in Python. Except when they are."
  • interfaces are mostly used to have a predictable outcome / enforce correctness of members when passing objects around. it would be great if python supported this as an option. it would also allow development tools to have better intellisense
  • interfaces are about memory management, primarily. They enforce the condition that the instantiated class that implements the interface, will have a memory footprint or 'signature' that will allow the interpreter/compiler to know with certainty the size of the object. I guess this isn't so necessary in Python due to dynamic typing and duck typing. If you want to define an interface, use ABC docs.python.org/3/library/abc.html, with which one marks classes as implementing an interface and which can be easily extended to provide the zope registry functionality.
  • An example would greatly improve this answer.
  • Yugghh, needing some module for what should be part of the language itself, or not used at all, IMO.
  • do you mean: if not server.version() == '1.0': raise ...? I don't realy get this line. An explaination would be welcome.