Decrorator

• decorator (link)

  • construction and apply

    • decorator in Python can be defined over any appropriate function using the @decorator_function_namesyntax to extend the functionality of the underlying function

      Untitled 1.png

    • Apply of decorator

      Untitled 2.png

  • build-in decorator

    • @property

      • a decorator for the property() function, then what is property()?

        #With attrib = property(fget, fset, fdel, doc) inside the class, we have an ability to get, set, del and document the value using the functions we designed
         
        class person:
            def __init__(self, name):
                self.__name=name
            def getname(self):
                print('getname() called')
                return self.__name
            def setname(self, name):
                print('setname() called')
                self.__name=name
            def delname(self):
                print('delname() called')
                del self.__name
            # Set property to use get_name, set_name
            # and del_name methods
            name=property(getname, setname, delname,doc='name of the person')
         
        p = Person('Stanley')
         
        # calls the getter
        print(p.name)
        # Prints Getting name: Stanley
         
        # calls the setter
        p.name = 'Bob'
        # Prints Setting name to Bob
         
        # calls the deleter
        del p.name
        # Prints Deleting name

      • How to use the decorator

        class Person():
            def __init__(self, value):
                self.hidden_name = value
         
            @property       # put the property before getting function
            def name(self):
                print('Getting name:')
                return self.hidden_name
         
            @name.setter    # use the name of getting function + '.setter' to indicate setting function
            def name(self, value):
                print('Setting name to', value)
                self.hidden_name = value
         
            @name.deleter
            def name(self): # use the name of getting function + '.deleter' to indicate setting function
                print('Deleting name')
                del self.hidden_name
         
        p = Person('Stanley')
         
        # calls the getter
        print(p.name)
        # Prints Getting name: Stanley
         
        # calls the setter
        p.name = 'Bob'
        # Prints Setting name to Bob
         
        # calls the deleter
        del p.name
        # Prints Deleting name

    • @classmethod

      • a decorator for the classmethod() function, then what is classmethod()?

        #classmethod() declares a class method, if it is not used, the method is belonged to the object
        class student:
            name = 'John'
         
            def show_name(self):
                print("The student's name is ",self.name)
         
        student.show_name = classmethod(student.show_name)
        student.show_name()  #output: The student's name is  John

      • How to use the decorator

        #classmethod() declares a class method, if it is not used, the method is belonged to the object
         
        class student:
            name = 'John'
         
            @classmethod
            def show_name(cls):   #use cls instead of self, because now we refer it to the current class
                print("The student's name is ",cls.name)
         
        student.show_name()  #output: The student's name is John

    • @staticmethod

      #static method = without referencing any object/ parameters, itself stands alone
      #Declares a static method in the class, which cannot have cls or self parameter/attributes.
      #The static method can be called using ClassName.MethodName() and also using object.MethodName().
      #It can return an object of the class.
       
      class Student:
          name = 'unknown' # class attribute
       
          def __init__(self):
              self.age = 20  # instance attribute
       
          @staticmethod
          def tostring():
              print('Student Class')
       
      #call from class
      >>> Student.tostring()  # output: 'Student Class'
      #call from object
      >>> std = Student()
      >>> std.tostring() # output: 'Student Class'