Basic Object-Oriented Programming (Advanced 4)

1. python's Object-Oriented Programming

Everything is an object, because I learned Java object-oriented programming ideas, Python is the same, so simply write this section.

What is Object-Oriented Programming

• Object-oriented programming is a programming paradigm
• Think of programs as calls between different objects
• Establishing an Object Model for the Present World

Basic Ideas of Object-Oriented Programming

• Class and real column
• Classes are used to define abstract types
• Instances are created based on class definitions

2. python defines classes and creates instances

# -*- coding:utf-8 -*-
class Person(object):
    pass

xiaoming = Person()
xiaohong = Person()
print xiaoming
print xiaohong
print xiaoming == xiaohong

3. Creating instance attributes in Python

class Person(object):
    pass
p1 = Person()
p1.name = 'Bart'

p2 = Person()
p2.name = 'Adam'

p3 = Person()
p3.name = 'Lisa'

L1 = [p1, p2, p3]
L2 = sorted(L1, lambda p1, p2: cmp(p1.name, p2.name))

print L2[0].name
print L2[1].name
print L2[2].name

4. Initialize instance properties in Python

When defining the Person class, you can add a special _init_() method to the Person class. When creating an instance, the init() method is called automatically. We can add the following attributes to each instance.

class Person(object):
    def __init__(self, name, gender, birth, **kw):
        self.name = name
        self.gender = gender
        self.birth = birth
        for k, v in kw.iteritems():
            setattr(self, k, v)
xiaoming = Person('Xiao Ming', 'Male', '1990-1-1', job='Student')
print xiaoming.name
print xiaoming.job

5. Access restrictions in Python

Python controls the permissions of attributes through the name of attributes. If an attribute begins with a double underscore (_), it cannot be accessed externally.

class Person(object):
    def __init__(self, name, score):
        self.name = name
        self.__score = score

p = Person('Bob', 59)

print p.name
print p.__score

6. Creating class attributes in Python

Each instance has its own, independent of each other, while class attributes have and only have one.

class Person(object):
    count = 0
    def __init__(self, name):
        Person.count = Person.count + 1
        self.name = name
p1 = Person('Bob')
print Person.count # 1

p2 = Person('Alice')
print Person.count # 2

p3 = Person('Tim')
print Person.count # 3

7. What about name conflicts between class attributes and instance attributes in Python

class Person(object):
    __count = 0
    def __init__(self, name):
        Person.__count = Person.__count + 1
        self.name = name
        print Person.__count

p1 = Person('Bob')
p2 = Person('Alice')

print Person.__count

8. Defining instance methods in Python

class Person(object):

    def __init__(self, name, score):
        self.__name = name
        self.__score = score

    def get_grade(self):
        if self.__score >= 80:
            return 'A'
        if self.__score >= 60:
            return 'B'
        return 'C'

p1 = Person('Bob', 90)
p2 = Person('Alice', 65)
p3 = Person('Tim', 48)

print p1.get_grade()
print p2.get_grade()
print p3.get_grade()

9. Methods in Python are also attributes

class Person(object):

    def __init__(self, name, score):
        self.name = name
        self.score = score
        self.get_grade = lambda: 'A'

p1 = Person('Bob', 90)
print p1.get_grade
print p1.get_grade()

10. Defining class methods in Python

Similar to attributes, methods are divided into instance methods and class methods.

class Person(object):
    __count = 0
    @classmethod
    def how_many(cls):
        return cls.__count
    def __init__(self, name):
        self.name = name
        Person.__count = Person.__count + 1

print Person.how_many()
p1 = Person('Bob')
print Person.how_many()