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Using getter, setter, and deleter functions are one way to implement encapsulation within Python where the state of class attributes can be handled within the class. These functions are useful in making sure that the data being handled is appropriate for the defined class functionality.

class Animal:
  def __init__(self, name):
    self._name = name
    self._age = None

  def get_age(self):
    return self._age

  def set_age(self, new_age):
    if isinstance(new_age, int):
      self._age = new_age
    else:
      raise TypeError

  def delete_age(self):
    print("_age Deleted")
    del self._age

Looking at the Animal class above there is an _age attribute with a single underscore. This notates it is intended to be used only within the module. There are then 3 methods related to age each with a different purpose. These define the getter, setter, and deleter of the specific property.

The first method related to age is a getter and returns self._age. The setter is implemented below that. It includes logic that ensures that the value passed to new_age is an integer. If so, self._age = new_age. If not, raise an error. This is useful and shows the power of using these functions for encapsulation.

The deleter is implemented below the setter. It outputs a confirmation message and uses the del keyword to delete the self._age attribute.

a = Animal("Rufus")
print(a.get_age()) # None

a.set_age(10)
print(a.get_age()) # 10

a.set_age("Ten") # Raises a TypeError

a.delete_age() # "_age Deleted"
print(a.get_age()) # Raises a AttributeError

Above we see a.get_age() gets the _age value, a.set_age(10) sets the value and a.delete_age() deletes the attribute entirely. A TypeError occurs with a.set_age("Ten") because the defined logic in the setter is looking only for an integer. An AttributeError occurs with a.get_age() after the attribute was deleted.

Instructions

Using a getter, setter, and the single underscore naming convention, the employees of the company will now be able to use their names. The single underscore attribute _name has been added to the Employee class. Names default to None unless a string argument is passed during instantiation.

Inside the Employee class:

Define a getter method called get_name() that returns the class attribute _name.

Add a setter method.

Inside the Employee class:

Define a setter method set_name that has an additional parameter for the name string and sets the class attribute _name.

Lastly, Add a deleter method.

Inside the Employee class:

Define a deleter method del_name that deletes the attribute.

Great job defining the getter and setter. Uncomment the code at the bottom of script.py to test out the getter, setter, and deleter.

Move on to the next exercise to wrap up the lesson!

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