accessify 0.1.0

Python class members accessibility levels.

accessify

Python class members accessibility levels.

• Getting started
  • What is accessify
  • Motivation
  • How to install
• Usage
  • Private
  • Protected
  • Other features
• Contributing
• References

Getting started

What is accessify

Access level modifiers determine whether other classes can use a particular field or invoke a particular method. Accessibility levels are presented from the box in the languages like C++, C# and Java.

class Car 
{
    private string StartEngine()
    {
        // Code here.
    }
}

But Python does not have this in the same way. accessify provides the functionality for Python projects that a bit close to the real accessibility levels.

Motivation

• We're all consenting adults here that is the part of the Python philosophy that relies on human factor instead of the interpreter.
• There is a Python convention that is to use an underscore prefix for protected and private members, that is a bit ugly. Isn't it? For instance, for the following piece of code that provides class private member.

class Car:

    def __start_engine(self, *args, **kwargs):
        pass

• Moreover, private and protected methods could be easily accessed outside the class. This is really a point to postpone the correct design of the system to the backlog, increasing the technical debt, sacrificed to fast feature delivering.

class Car:

   def _start_engine(self, *args, **kwargs):
       pass
       
   def __start_engine(self, *args, **kwargs):
       pass


car = Car()
car._start_engine()
car._Car__start_engine()

How to install

Using pip install the package from the PyPi.

$ pip3 install accessify

Usage

Private

• Private members are accessible only within the body of the class.

In this example, the Car class contains a private member named start_engine. As a private member, they cannot be accessed except by member methods. The private member start_engine is accessed only by way of a public method called run.

from accessify import private


class Car:

    @private
    def start_engine(self):
        return 'Engine sound.'

    def run(self):
        return self.start_engine()


if __name__ == '__main__':
    car = Car()

    assert 'Engine sound.' == car.run()

    car.start_engine()

The code above will produce the following traceback.

Traceback (most recent call last):
  File "examples/access/private.py", line 24, in <module>
    car.start_engine()
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/accessify/main.py", line 92, in private_wrapper
    class_name=instance_class.__name__, method_name=method.__name__,
accessify.errors.InaccessibleDueToItsProtectionLevelException: Car.start_engine() is inaccessible due to its protection level

Test it out using the examples. Get the example that contains the code above by curl and run it by python3.

$ curl -L https://git.io/fhASP > private.py
$ python3 private.py

• Child classes cannot access parent private members.

In this example, the Car class contains a private member named start_engine. As a private member, they cannot be accessed from the child classes, Tesla in our case. So overridden method run by Tesla class cannot use the parent's start_engine member.

from accessify import private


class Car:

    @private
    def start_engine(self):
        return 'Engine sound.'


class Tesla(Car):

    def run(self):
        return self.start_engine()


if __name__ == '__main__':
    tesla = Tesla()
    tesla.run()

The code above will produce the following traceback.

Traceback (most recent call last):
  File "examples/inheritance/private.py", line 23, in <module>
    tesla.run()
  File "examples/inheritance/private.py", line 18, in run
    return self.start_engine()
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/accessify/main.py", line 94, in private_wrapper
    class_name=class_contain.__name__, method_name=method.__name__,
accessify.errors.InaccessibleDueToItsProtectionLevelException: Car.start_engine() is inaccessible due to its protection level

Test it out using the examples. Get the example that contains the code above by curl and run it by python3.

$ curl -L https://git.io/fhASX > inheritence_private.py
$ python3 inheritence_private.py

Protected

• A protected member is accessible within its class and by derived class instances.

In this example, the Car class contains a protected member named start_engine. As a protected member, they cannot be accessed except by member methods. The protected member start_engine is accessed only by way of a public method called run.

from accessify import protected


class Car:

    @protected
    def start_engine(self):
        return 'Engine sound.'

    def run(self):
        return self.start_engine()


if __name__ == '__main__':
    car = Car()

    assert 'Engine sound.' == car.run()

    car.start_engine()

The code above will produce the following traceback.

Traceback (most recent call last):
  File "examples/access/protected.py", line 21, in <module>
    car.start_engine()
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/accessify/main.py", line 134, in protected_wrapper
    class_name=instance_class.__name__, method_name=method.__name__,
accessify.errors.InaccessibleDueToItsProtectionLevelException: Car.start_engine() is inaccessible due to its protection level

Test it out using the examples. Get the example that contains the code above by curl and run it by python3.

$ curl -L https://git.io/fhASM > protected.py
$ python3 protected.py

• Child classes have access to those protected members.

In this example, the Car class contains protected member named start_engine. As protected member, they can be accessed from the child classes, Tesla in our case. So overridden method run by Tesla class can use the parent's start_engine member.

from accessify import protected


class Car:

    @protected
    def start_engine(self):
        return 'Engine sound.'


class Tesla(Car):

    def run(self):
        return self.start_engine()


if __name__ == '__main__':
    tesla = Tesla()

    assert 'Engine sound.' == tesla.run()

The code will work without errors.

Test it out using the examples. Get the example that contains the code above by curl and run it by python3.

$ curl -L https://git.io/fhASD > inheritence_protected.py
$ python3 inheritence_protected.py

Other features

• The accessify decorator removes private and protected members from class dir.

from accessify import accessify, private


@accessify
class Car:

    @private
    def start_engine(self):
        return 'Engine sound.'

if __name__ == '__main__':
    car = Car()

    assert 'start_engine' not in dir(car)

Test it out using the examples. Get the example that contains the code above by curl and run it by python3.

$ curl -L https://git.io/fhASy > dir.py
$ python3 dir.py

Contributing

Clone the project and install requirements.

$ git clone [e-mail]:dmytrostriletskyi/accessify.git && cd accessify
$ pip3 install -r requirements-dev.txt
$ pip3 install -r requirements-tests.txt

When you will make changes, ensure your code pass the checkers and is covered by tests using pytest.

If you are new for the contribution, please read:

• Read about pull requests — https://help.github.com/en/articles/about-pull-requests
• Read how to provide pull request — https://help.github.com/en/articles/creating-a-pull-request-from-a-fork
• Also the useful article about how to contribute — https://akrabat.com/the-beginners-guide-to-contributing-to-a-github-project/

References

Check it out to familiarize yourself with class members accessibility levels:

• C# accessibility levels — https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/accessibility-levels
• Java accessibility levels — https://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html