Python Strict Interfaces

Installation

pip install strict-interfaces

Design Goals

• Be as strict as possible
• Fail on import time
• Do not mess with object and/or type inheritance
• Possibility to integrate in CPython Core
• Ability to use "out of the box" regardless support in an interpreter

Features

• Special keyword implements on the class definition
• Multiple interface implementation
• Implicit interface implementation
• Interface inheritance with overloading being restricted
• Special isimplementation function similar to issubclass
• Partial issubclass support (see below)
• It's restricted to create an interface instance
• It's restricted to inherit from object and interface at the same time

Usage

Explicit implementation

class TestInterface(interfaces.interface):
    def method(self, arg: typeT1) -> typeT2:
        pass

class TestClass(interfaces.object, implements=[TestInterface]):
    def method(self, arg: typeT1) -> typeT2:
        pass

Raises when is not implemented

class TestInterface(interfaces.interface):
    def method(self, arg):
        pass

class TestClass(interfaces.object, implements=[TestInterface]):
    pass

Implicit implementation and run-time check

class TestInterfaceA(interfaces.interface):
    def method_a(arg: typeT1) -> typeT1:
        pass

class TestInterfaceB(interfaces.interface):
    def method_b(arg: typeT2) -> typeT2:
        pass

class TestClass:
    def method_a(arg: typeT1) -> typeT1:
        pass

    def method_b(arg: typeT2) -> typeT2:
        pass

assert interfaces.isimplementation(TestClass, (TestInterfaceA, TestInterfaceB))

isimplementation checks whether all interfaces are implemented

class TestInterfaceA(interfaces.interface):
    def method_a(arg: typeT1) -> typeT1:
        pass

class TestInterfaceB(interfaces.interface):
    def method_b(arg: typeT2) -> typeT2:
        pass

class TestClass:
    def method_a(arg: typeT1) -> typeT1:
        pass

# NOTE: In this case `isimplementation` behaves different than `issubclass`
assert not interfaces.isimplementation(TestClass, (TestInterfaceA, TestInterfaceB))
assert issubclass(TestClass, (TestInterfaceA, TestInterfaceB))

Contributing

Pull requests, feature requests, and bug reports are always welcome!

github.com/lig/python-interfaces