Python Object-oriented programming-classes and instances

1        Object-Oriented programming

Object-Oriented Programming:

Object-Oriented programming -- Object orientedprogramming

OOP takes objects as the basic unit of a program, and an object contains functions for data and manipulating data.

process-oriented procedures The design treats the computer program as a series of command sets, that is, the sequence of a set of functions executes. In order to simplify the program design, the process will continue to cut the function into sub-function, that is, the large function by cutting into small block function to reduce the complexity of the system.

Object-oriented programming treats a computer program as a set of objects , and each object can receive messages from other objects and process them, and the execution of a computer program is a series of messages passing between objects.

all data types can be treated as objects, as well as custom objects, and custom object data types are object-oriented classes ( class ) Concept of .

When it comes to classes, you naturally think of instances, classes are abstractions of data types, and instances are concrete (personal understanding) of classes.

>>> std1 = {' name ': ' Michael ', ' Score ': 98}

>>> std2 = {' name ': ' Bob ', ' Score ': 81}

>>>

>>> def print_score (STD):-- print student's name and score

... print ('%s:%s '% (std[' name '], std[' score '))

...

>>> Print_score (STD1)

Michael:98

>>> Print_score (STD2)

bob:81

according to the object-oriented program design idea, this student should be regarded as object, abstract into class;

>>> classstudent (object):-- Define class

... def __init__ (self, name, score):

... self.name = name

... self.score = Score

... def print_score (self):-- Define method

... print ('%s:%s '% (Self.name, Self.score))

...

>>> bart = Student (' Bart Simpson ', 59)

>>> Lisa = Student (' Lisa Simpson ', 87)

>>> Bart.print_score () -- method of invoking the object, a concrete object -- instance

Bart simpson:59

>>> Lisa.print_score ()

Lisa simpson:87

the object-oriented design idea is to abstract out Class, create Instancebased on class.

1.1   Classes and Instances1.1.1   Classes and Instances

>>> class Student (object):--class defines the class's keyword,Student class name (beginning with uppercase),(object) which class inherits from

... pass

...

>>> Student

<class ' __main__. Student ' >

>>> Bart = Student () -- Create an instance from a class

>>> Bart

<__main__. Student Object at0x2b7d2fd759e8>

if there is no appropriate inheritance class, use the Object class , which is the class that all classes will eventually inherit .

you are free to bind attributes to an instance variable, for example, Bart binds a name property:

>>> bart.name = ' Bart Simpson '

>>> Bart.name

' Bart Simpson '

because the class acts as a template, when you create a class, you can force the properties that must be bound to be filled in- through the init method

>>> class Student (object):

... def __init__ (self, Name,score):--init method, The first parameter of Init is always self

... self.name = name

... self.score = Score

...

within the __init__ method, it is possible to bind various properties to self , because The individual points to the created instance itself .

The Init method exists , and when you create an instance, you must fill in the specified parameters, but self does not need to be passed in, andPython fills in.

>>> Bart = Student (' Daidai ')-- must fill in the specified parameters, mandatory

>>> Bart.name--name,score becomes an object's property

' Daidai '

>>> Bart.score

99

>>> bart.self-- can't specify self so

Traceback (most recent):

File "<stdin>", line 1, in <module>

Attributeerror: ' Student ' object had Noattribute ' self '

>>> bart.grade = ' A '-- new attribute grade

>>> Bart.grade

A

There is no difference between a class method and a normal function, so you can still use default parameters, variable parameters, keyword arguments, and named keyword Parameters .

1.1.2   Data Encapsulation

>>> class Student (object):

... def __init__ (self, Name, score):

... self.name = name

... self.score = Score

... def print_score (self):--Print_score method

... print ('%s:%s '% (Self.name, Self.score))

... def get_grade (self):--get_grade Method

... if Self.score >= 90:

... print (' A ')

... elif self.score >= 70:

... print (' B ')

.. else:

.. print (' C ')

...

define a method, the first argument is self, and the other is consistent with the function.

>>> Daidai = Student (' Daidai ', 99)

>>> Daidai.print_score ()-- call on instance variable

daidai:99

>>> Daidai.get_grade ()

A

This is the definition of the implementation class and the definition of its method, which implements the encapsulation of the class.

A method is a function that is bound to an instance, and unlike a normal function, a method can directly access the data of an instance.

Python allows you to bind any data to an instance variable , that is, for two instance variables, although they are different instances of the same class, the variable names you have may be different.

>>> Daidai.age = 8

>>> Daidai.age

8

>>> Xiongxiong.age-- This instance variable is not bound

Traceback (most recent):

File "<stdin>", line 1, in <module>

Attributeerror: ' Student ' object had Noattribute ' age '

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Python Object-oriented programming-classes and instances