Class 1 Creation and Use
- 1 class creation
- Class 2 use
2 properties and methods of the class

1, the creation and use of classes

class creation
class usage

(1), the creation of the class

The general form of a class is as follows:

class <类名>(父类名):
    类中的函数等

Example of class definition:

class myClass:
    pass

(2), the use of classes

After a class is defined, it needs to be instantiated before it can be used. After the class is instantiated, an instance of the class is generated ; a class can be instantiated
by adding parentheses to the class;
a class can be instantiated with multiple instances, and there is no difference between instances Influence each other.

Example of instantiation of a class:

class MyClass:
    'MyClass Help'

myClass = MyClass()
print(myClass.__doc__)
help(myClass)

Running result:
MyClass Help
Help on MyClass in module main object:

2. Class attributes and methods

class method
class properties
class method vs static method

(1), class methods

The first parameter in the method must be self and cannot be omitted;

The method call needs to instantiate the class and call it in the form of instance name.method name;

The overall indentation is one unit, indicating the content of the class;

Examples of methods in a class:

class MyClass :
    def function1(self):
        print('This is function1')

    def function2(self):
        print('This is function2')

myClass = MyClass()
myClass.function1()
myClass.function2()

Running result:
This is function1
This is function2

When calling the method, you don't have to pass the self parameter;

The __init__() method is used to initialize related data when the class is instantiated;

When a method defined in this class is called from a class, the self parameter should not be passed in the parameter list of the call

class MyClass :
    def __init__(self, x = 10, y = 20):
        self.x = x
        self.y = y

    def calcAdd(self):
        return self.getX() + self.getY()

    def getX(self):
        return self.x

    def getY(self):
        return self.y

myClass = MyClass(22, 30)
print(myClass.calcAdd())

Running result:
52

(2), the attributes of the class

In Python, the class class definition attribute is to use it directly first, and the attribute can be defined in the construction method; the defined attribute
can also be used in other methods in the class;

There are two types of class attributes in the python language, similar to member variables and static member variables in C++:

Instance attribute: use instance name.attribute name when using

Class attribute: use class name.attribute name when using

Examples of properties of a class:

class MyClass :
    class_name = 'MyClass'
    def __init__(self, x = 10, y = 20, name = 'MyClass'):
        self.x = x
        self.y = y
        MyClass.class_name = name

    def calcAdd(self):
        return self.getX() + self.getY()

    def getX(self):
        return self.x

    def getY(self):
        return self.y

myClass = MyClass(22, 30, 'TestClass')
print(myClass.x)
print(MyClass.class_name)

Running result:
22
TestClass

(3), class method and static method

Class methods are of the following types:

instance method
class method
static method

Static methods are decorated with the decorator @staticmethod and have no default parameters;

The class method is decorated with the decorator @classmethod and must have the default parameter "cls"

When calling, no instantiation is required; directly use the class name. Method name () call

Examples of class methods and static methods:

class MyClass :
    class_name = 'MyClass'
    def __init__(self, x = 10, y = 20, name = 'MyClass'):
        self.x = x
        self.y = y
        MyClass.class_name = name

    # 类的静态方法    
    @staticmethod
    def getClassName():
        print(MyClass.class_name)
    # 类方法
    @classmethod
    def getClassName2(cls):
        print(MyClass.class_name)

MyClass.getClassName()      
myClass = MyClass(22, 30, 'TestClass')
MyClass.getClassName2()

Running result:
MyClass
TestClass

8. Classes in Python (1)