stay Python Object oriented , Some properties of the class , If in use , Don't want to be directly accessed by the outside world , You can set this property to private , That is, only the current class holds , Then expose to the outside world an access function , To achieve indirect access to object properties , This is the encapsulation of data in the class .
If the properties in the class do not want to be directly accessed by the outside world , You can add two underscores in front of the attribute __, In this case, this property is called private property , That is, private member variables .
The essence of encapsulation ： Is the privatization of attributes .
Can only be accessed directly inside a class , Not directly accessible from the outside .
1） Property is not privatized ：
# 1. When properties are not privatized
class Student():
def __init__(self, name, age):
self.name = name
self.age = age
def tellMe(self):
print(f" Hello everyone , I am a {self.name}, Age {self.age}")
# Create objects
stu = Student(" The Monkey King ", 18)
# Through object . Member functions , Call the function and access the member variables in the object
stu.tellMe()
# Through object . attribute , Directly access the properties in the object
print(f" Hello everyone , I am a {stu.name}, Age {stu.age}")
# Directly access the properties of an object through an object , And assign a value to the property
stu.name = " Monkey King "
print(stu.name) # Monkey King
"""
Output results ：
Hello everyone , I'm the monkey king , Age 18
Hello everyone , I'm the monkey king , Age 18
Monkey King
As you can see, you can access .
"""
2） Property is privatized ：
# 2. When the property is privatized
class Student():
def __init__(self, name, age):
self.name = name
# Privatization age attribute
self.__age = age
def tellMe(self):
print(f" Hello everyone , I am a {self.name}, Age {self.__age}")
# Create objects
stu = Student(" The Monkey King ", 18)
# Through object . Member functions , Call the function and access the member variables in the object
# You can access the private member variables in the current object
# Output ： Hello everyone , I'm the monkey king , Age 18
stu.tellMe()
# Through object . attribute , Directly access the properties in the object
# Report errors ：
# AttributeError: 'Student' object has no attribute '__age'
# print(f" Hello everyone , I am a {stu.name}, Age {stu.__age}")
# Directly through the object . attribute , Modify the attribute value of member variable
# Sure
stu.name = " Monkey King "
print(stu.name) # Monkey King
# result ： Hello everyone , I'm the saint of heaven , Age 18
stu.tellMe()
# Directly through the object . attribute , Modify the property value of private member variable
# Output results
stu.__age = 30
print(stu.__age) # 30
# result ： Hello everyone , I'm the saint of heaven , Age 18
# But by calling methods in the object , View the private properties of the object
# The results have not changed , still 18
stu.tellMe()
"""
But we go through __dict__ Property view stu All members of the object ：
{'name': ' Monkey King ', '_Student__age': 18, '__age': 30}
You can see that we have not modified the original properties '_Student__age': 18,
But to stu Object adds a new attribute '__age': 30.
So we don't have private member variables age Reassignment succeeded .
Only '_Student__age': 18 Why do you mean private variables age,
We will explain the principle of private members below .
"""
print(stu.__dict__)
explain ： Properties starting with double underscores , Is a hidden property of an object , Hidden properties can only be accessed inside a class , Cannot access through object
class Student():
def __init__(self, name, age):
self.name = name
# Privatize member properties
self.__age = age
def tellMe(self):
print(f" Hello everyone , I am a {self.name}, Age {self.__age}")
"""
Actually hide （ Privatization ） Attributes are just Python Automatically changed a name for the property
It's actually changing the name to ,_ Class name __ Property name
such as __age -> _Student__name,
That is to add... Before the original variable name _ Class name .
"""
# Create objects
stu = Student(" The Monkey King ", 18)
# result ： Hello everyone , I'm the monkey king , Age 18
stu.tellMe()
# Directly through the object . attribute , Modify the private member variable of the object
# You can see from the print results below , The modification was successful
stu._Student__age = 30
# result ： Hello everyone , I'm the monkey king , Age 30
stu.tellMe()
summary ：
Python in , did not The real meaning Of private , In fact, some special processing has been done for the name of member variables , Make it inaccessible to the outside world .
So it is defined as double underline
__The properties of the beginning , In fact, it can still be accessed externally .But we usually don't recommend accessing private properties like this .
xxx： Common variables ._xxx： Use _ The first attribute is a protected variable , Do not modify without special needs .__xxx： Use double _ The first attribute is a private variable , Not directly accessible from the outside .__xxx__： Built in variables of the system .xx_: Single post underline , Used to avoid and Python Keywords conflict .Example ：
class Student():
def __init__(self, name, age, gender):
# Add an underscore in front of the variable , It belongs to a special variable , The variable is considered protected
self._name = name
# Add a double underline before the variable . Represents the definition of private variables .
# characteristic ： Object cannot be used directly
self.__age = age
# Add two underscores before and after the variable , It belongs to a special variable , It is generally believed that such variables are built-in variables or built-in functions of the system
# characteristic ： You can also directly access... Outside the class , But not recommended
self.__gender__ = gender
stu = Student(" Tang's monk ", 66, " male ")
print(stu._name) # Tang's monk
print(stu.__gender__) # male
（1） The way ：
How to get （ modify ） Private properties in the object ？
Need to provide a
getter()andsetter()Method enables external access to properties .
getter()Method is used to get the specified property in the object .getter()The specification of the method is namedget_ Property name.
setter()Method is used to set the specified property in the object .setter()The specification of the method is namedset_ Property name.
（2） Format ：
getter() Method ： There will be a return value .
def get_xxx(self):
return self. Property name
setter() Method ： no return value , But the method has one more parameter .
def set_xxx(self, Parameter name ):
self. Property name = The value of the parameter name
（3） Example ：
class Student():
def __init__(self, name, age):
# Common variables
self.name = name
# Private variables
self.__age = age
def tellMe(self):
print(f" Hello everyone , I am a {self.name}, Age {self.__age}")
def get_name(self):
"""
get_name() To get objects name attribute
"""
return self.name
def set_name(self, name):
"""
set_name() Used to set the object's name attribute
"""
self.name = name
def get_age(self):
return self.__age
def set_age(self, age):
if age > 0:
self.__age = age
# Create objects
stu = Student(" The Monkey King ", 18)
# Output results ： Hello everyone , I'm the monkey king , Age 18
stu.tellMe()
# Modify attribute values
stu.set_name(" Monkey King ")
stu.set_age(30)
# Print attribute values
# The result is : Hello everyone , I'm the saint of heaven , Age 30
stu.tellMe()
print(f" Hello everyone , I am a {stu.get_name()}, Age {stu.get_age()}")
"""
Private attributes can only be used inside a class , Object cannot be used directly , But we can call or modify private properties by defining public methods inside the class , Then the object uses... When calling the public method
"""
（4） summary ：
getter() Methods and setter() Method to get or set the property value , We often program like this in our daily development .getter() Methods and setter() Method , It's a good way to control whether a property is read-only ,setter() Method ,getter() Method .setter() Method to set properties , You can add data validation , Make sure the value of the data is correct , Such as ： def set_age(self, age):
if age > 0:
self.__age = age
getter() Method to get properties , Or use setter() Method to set properties , You can read and modify properties at the same time , Do some other processing of the data .
