Python practical Notes (22) object-oriented programming--instance properties and class properties

Because Python is a dynamic language, an instance created from a class can be arbitrarily bound to a property.

The way to bind properties to an instance is through an instance variable, or through a self variable:

class Student(object):    def __init__(self, name): self.name = names = Student(‘Bob‘)s.score = 90

But what if the Student class itself needs to bind a property? You can define a property directly in class, which is a class attribute and belongs to Student all classes:

class Student(object):    name = ‘Student‘

When we define a class property, this property is categorized as all, but all instances of the class can be accessed. To test:

>>>ClassStudent(object):... Name =' Student ' ...>>> s = Student () # create instance S>>> print (s.name) # print the Name property because the instance does not have a Name property, so it continues to find the Name property of class Student>> > Print (student.name) # Print class Name property Student >>> s.name =  ' Michael ' # to instance Bindings Name property >>> print (s.name) # because instance attribute precedence is higher than class property, it masks the name property of the class Michael>>> print (Student.name) span class= "comment" ># but the class properties do not disappear, Student>>> del s.name # if the Name property of the instance is deleted >>> print ( S.name) # call S.name again, because the name property of the instance is not found, the Name property of the class is displayed student     

As can be seen from the above example, when writing a program, do not use the same name for instance properties and class properties, because instance properties of the same name will mask the class properties, but when you delete an instance property and then use the same name, the class attribute is accessed.

Python practical Notes (22) object-oriented programming--instance properties and class properties