A detailed explanation of the use of class and variables in python

The definition of variables in python is very flexible and easy to be confused, especially for the definition of variables in class. How to define and use variables in classes is the key to maintain code and ensure code stability.

#!/usr/bin/python
#encoding:utf-8
 
global_variable_1 = 'global_variable'
 
class MyClass():
  class_var_1 = 'class_val_1' # define class variable here
  def __init__(self, param):
    self.object_var_1 = param # define object variable here
    self.object_var_2 = 'object_val_2' # define object variable here
    self.object_func3()
 
  def object_func1(self, param):
    local_var_1 = param # define lcoal variable here
    local_var_2 = 'local_val_2' # define local variable here
    self.internal_var_1 = 'internal_val_1' # define internal variable here
    print(local_var_1) # we can use local variable of current here
    print(local_var_2) # we can use local variable of current here
    print(MyClass.class_var_1) # we can use class variable here, but you have using class name ass prefix
    print(self.class_var_1) # we can use class variable as object variable here
    print(self.object_var_1) # we can use object variable here
    print(self.object_var_2) # we can use object variable here
    print(self.internal_var_1) # we can use internal variable here
    #print(local_var_3) # we can't use local variable in another function
    print(global_variable_1) # we can use global variable here
 
  def object_func2(self, param='func_val_1'):
    local_var_3 = param # define local variable here
    print(local_var_3) # we can use lcoal variable here
    print(self.internal_var_1) # we can use internal variable defined in class_func1, but you have to call class_func1 first
    print(MyClass.class_var_1) # we can use class variable here, but you have using class name ass prefix
    print(self.class_var_1) # we can class variable here
    print(self.object_var_1) # we can use object variable here
    print(self.object_var_2) # we can use object variable here
    print(global_variable_1) # we can use global variable here
 
 
  def object_func3(self, param='func_val_1'):
    self.object_var_3 = param # because this function called in construction function, so this is defined as object variable, not internal variable
    self.object_var_4 = 'object_val_4' # because this function called in construction function, so this is defined as object variable, not internal variable
    print(global_variable_1) # we can use global variable here
  
  # define class function
  def class_func4():
    print(MyClass.class_var_1)
    print(global_variable_1) # we can use global variable here
 
if __name__ == '__main__':
  myObject = MyClass('object_val_1')
  print(MyClass.class_var_1) # we can use class variable directly here
  #print(MyClass.object_var_1) # we can't use object variable here
  print(myObject.object_var_1) # we can use object variable here
  print(myObject.object_var_2) # we can use object variable here
  print(myObject.object_var_3) # we can use object variable here
  print(myObject.object_var_4) # we can use object variable here
  #print(myObject.internal_var_1) # we can't use internal variable as object variable here
  MyClass.class_func4() # we can use class function here
  #MyClass.object_func2(myObject, 'local_var_3') # internal variable can't be used in this function
  myObject.object_func1('local_var_1') # call first function
  myObject.object_func2('local_var_3') # call second function
  print(global_variable_1) # we can use global variable here

Simply wrote a test applet, enumerated a variety of situations, there is no way to enumerate all, but most of the situation should have been included.

1. Class variable: It can be accessed by class name or self of object, and can be reached both inside and outside the class, such as class_var_1

2. Object variables: Variables that can be used through self of an object, and variables that are first assigned to self through constructor1 will become object variables, such as object_var_1, object_var_2, object_var_3, object_var_4

3. Internal variables: can be defined in a function and prefixed with self. After the defined function is called for the first time, it can be used in the functions of subsequent objects, such as internal_var_1

4. Local variables: Variables defined and used inside a function are reclaimed after they are used and are not visible to the class and object

5. Global variable: Any snippet of code defined outside a class or function and scoped after the variable is defined, such as global_var_1

The above is based on my own test conclusions, if there is something wrong, can help correct.