Encapsulation 封装 of class in Python

In software development, encapsulation is one of the four foundational pillars of OOP.

Encapsulation 封装 of class is a concept of bundling of data and the methods that operate on that data into a single unit.

Private Attributes (Data hiding) / Behaviour

For example, a mobile phone, may allow all of the user to have a feature like taking photograph, calling to others, connect to the internet, ...

However a phone would have it hidding data (Private attributes) like control the voltage for the processor, memory management, drivers information, which is not open to the user.

• So, there is a 2 private class members which is private attributes and private behaviour.

Usage

# Private attributes
__attrs = ""

# Private behaviour/ method
def __fun(x):
    ...

• Add double undersocre for the variable and methods. (__var = x) / (def __f(x):)

Example

class-private-attribute-behaviour.py

class Phone:
    phone_name = None
    IMEI = None
    __maximum_voltage = 1.25
    
    def __init__(self, phone_name, IMEI):
        self.phone_name = phone_name
        self.IMEI = IMEI
    
    def connect_to_network(self, status: bool):
        if status:
            print("Connected to network")
        else:
            print("Disconnect from network connection")
            
    def __run_on_single_core(self):
        print(f"Phone is run on single core only. Maximum voltage for cpu is {self.__maximum_voltage}v")
        
    print(__maximum_voltage)
    
p1 = Phone("Star", 1879986652080)

print(p1.phone_name, p1.IMEI)
print(p1.__maximum_voltage)

Output:

1.25
Star 1879986652080
Traceback (most recent call last):
  File "d:\jiale-note\demo-examples\Python\Language\class-private-attribute-behaviour.py", line 21, in <module>
    print(p1.__maximum_voltage)
          ^^^^^^^^^^^^^^^^^^^^
AttributeError: 'Phone' object has no attribute '__maximum_voltage'. Did you mean: '_Phone__maximum_voltage'?

ERROR

• The private attributes / behaviour can't be access on outside of the class.
• However these private attributes / behaviour can be access on outside of the class, only when they are use by other attributes / behaviour that are not private.

class-private-attribute-behaviour.py

class Phone:
    phone_name = None
    IMEI = None
    
    # Private attr
    __maximum_voltage = "1.25"
    
    def __init__(self, phone_name, IMEI):
        self.phone_name = phone_name
        self.IMEI = IMEI
    
    def connect_to_network(self, status: bool):
        if status:
            print("Connected to network")
        else:
            print("Disconnect from network connection")
            
    # Private behaviour        
    def __run_on_single_core(self):
        print(f"Phone is run on single core only. Maximum voltage for cpu is {self.__maximum_voltage}v")
        
    def battery_level(self, percentage_of_battery: float):
        if percentage_of_battery <= 20:
            # Using Private behaviour for a non-private function
            self.__run_on_single_core()
        else:
            print("Multi-core is enabling.")
    
    # use inside of a class
    print(__maximum_voltage)
    
p1 = Phone("Star", 1879986652080)

print(p1.phone_name, p1.IMEI)
p1.connect_to_network(True)
p1.battery_level(49)
p1.battery_level(19.334)

Output:

1.25
Star 1879986652080
Connected to network
Multi-core is enabling.
Phone is run on single core only. Maximum voltage for cpu is 1.25v