Property Decorators

https://www.youtube.com/watch?v=jCzT9XFZ5bw&list=PL-osiE80TeTt2d9bfVyTiXJA-UTHn6WwU

Getters - @property
Setters - @<prop_name>.setter
Deleters - @<prop_name>.deleter

Scenario without Getters and Setters

class Employee:

    def __init__(self, first, last):
        self.first = first
        self.last = last
        self.email = f'{self.first}.{self.last}@email.com'.lower()

    def fullname(self):
        return f'{self.first} {self.last}'

emp_1 = Employee('John', 'Doe')

print(emp_1.first) # => John
print(emp_1.email) # => john.doe@email.com
print(emp_1.fullname()) # => John Doe

emp_1.first = 'Jim'

print(emp_1.first) # => Jim
print(emp_1.email) # => john.doe@email.com # ! Observe that this is still John
print(emp_1.fullname()) # => Jim Doe

Problem #1

Observe that after changing emp_1.first to Jim...
The emp_1.email still have the John

Workaround

class Employee:

    def __init__(self, first, last):
        self.first = first
        self.last = last
-       self.email = f'{self.first}.{self.last}@email.com'.lower()

+   def email(self):
+       return f'{self.first}.{self.last}@email.com'.lower()

    def fullname(self):
        return f'{self.first} {self.last}'

 emp_1 = Employee('John', 'Doe')

 print(emp_1.first) # => John
+print(emp_1.email()) # => john.doe@email.com
-print(emp_1.email) # => john.doe@email.com
 print(emp_1.fullname()) # => John Doe

 emp_1.first = 'Jim'

 print(emp_1.first) # => Jim
+print(emp_1.email()) # => jim.doe@email.com
-print(emp_1.email) # => jim.doe@email.com
 print(emp_1.fullname()) # => Jim Doe

In this approach, when we update the emp_1.first, then it will also automatically update emp_1.email()

Problem #2 and Solution

Notice, also, emp_1.email is changed to emp_1.email()

After this approach, anyone that uses our existing code will have to update their code.
So in order to continuously accessing the email as an attribute rather than a method email()...

We will use @property decorator

Getters

class Employee:

    def __init__(self, first, last):
        self.first = first
        self.last = last

+   @property
    def email(self):
        return f'{self.first}.{self.last}@email.com'.lower()

    def fullname(self):
        return f'{self.first} {self.last}'

 emp_1 = Employee('John', 'Doe')

 print(emp_1.first) # => John
+print(emp_1.email) # => john.doe@email.com
-print(emp_1.email()) # => john.doe@email.com
 print(emp_1.fullname()) # => John Doe

 emp_1.first = 'Jim'

 print(emp_1.first) # => Jim
+print(emp_1.email) # => jim.doe@email.com
-print(emp_1.email()) # => jim.doe@email.com
 print(emp_1.fullname()) # => Jim Doe

It works also on the fullname()

class Employee:
    ...
-   @property
    def fullname(self):
        return f'{self.first} {self.last}'

 emp_1 = Employee('John', 'Doe')
-print(emp_1.fullname())
+print(emp_1.fullname)

Next Scenario

When we update emp_1.fullname with a new value
Then we also want to update the first and last name.

To solve this, we need to create a @<prop>.setter decorator

Setters

class Employee:
    ...

    @property
    def fullname(self):
        return f'{self.first} {self.last}'

+   @fullname.setter
+   def fullname(self, new_name):
+       first, last = new_name.split(' ')
+       self.first = first
+       self.last = last

 print(emp_1.first) # => Jim
 print(emp_1.email) # => jim.doe@email.com
 print(emp_1.fullname) # => Jim Doe

+emp_1.fullname = 'Ji-Eun Lee'

+print(emp_1.first) # => Ji-eun
+print(emp_1.email) # => ji-eun.lee@email.com

Deleters

class Employee:
    ...

    @property
    def email(self):
        if self.first is None or self.last is None:
            return None

        return f'{self.first}.{self.last}@email.com'.lower()

    @property
    def fullname(self):
        return f'{self.first} {self.last}'

    @fullname.deleter
    def fullname(self):
        print('Name deleted!')
        self.first = None
        self.last = None

print(emp_1.first) # => Ji-eun
print(emp_1.email) # => ji-eun.lee@email.com

del emp_1.fullname

print(emp_1.first) # => None
print(emp_1.last) # => None
print(emp_1.email) # => None

Name		Name	Last commit message	Last commit date
.gitignore		.gitignore
README.md		README.md
main.py		main.py

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Property Decorators - Getters, Setters, and Deleters