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Encapsulation is the process of making methods and data hidden inside the object they relate to. Languages accomplish this with what are called access modifiers like:

  • Public
  • Protected
  • Private

In general, public members can be accessed from anywhere, protected members can only be accessed from code within the same module and private members can only be accessed from code within the class that these members are defined.

Python doesn’t have any inbuilt mechanism to prevent access from any member (i.e. all members are public in Python). However, there is a common convention amongst developers to use a single underscore self._x to indicate that a member is protected. Accessing a protected member outside of the module will not cause an error, it is added by developers to inform other developers that they should be careful when accessing this member in such a manner.

Similarly, we can declare a member as private with two leading underscores self.__x. This is more than just a convention in Python because of a mechanism called name mangling. Members that are preceded with two underscores have their names modified in the background to obj._Classname__x. While they can still be publicly accessed, the purpose of this mechanism is to prevent clashing member names of any inheriting classes that might define a member of the same name.

Note that this is different from the dunder methods we discussed earlier. A dunder method has two leading and two trailing underscores and is treated differently than a private member. One important difference is that dunder method names are not mangled.

Instructions

1.

The Employee class contains one attribute id. An instance variable e is defined and then passed to the function dir() which is output to the console.

dir() is a built-in Python function that returns a list of all class members, including dunder methods.

When you run the code, you will see a list of class members with id as the last element.

2.

Now add an attribute that uses the single underscore naming convention.

Inside the Employee class .__init__() method:

  • Define the single underscore variable_id and set it equal to whatever you want

When you run the code you can see _id as the second to last element in the output list.

3.

Now define a variable using the double-underscore.

Inside the Employee class .__init__() method:

  • Define the double underscore variable __id and set it equal to whatever you want

When you run the code you can see a new variable _Employee__id as the first element in the output list. This is the result of name-mangling the variable self.__id.

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