python daily learning 1

 

# -*- coding: UTF-8 -*-

class Robot:
    population = 0

    def __init__(self, name):
        # init function is similar to constructor in java
        # Added a variable name to the instance, the value is the incoming name
        self.name = name
        print "(Initializing {})".format(self.name)
        Robot.population += 1

    # The self here is the same as the self of the __init__() function, and the name can also be obtained
    def die(self):
        print "{} is being destoryed!".format(self.name)
        Robot.population -= 1

        if  Robot.population == 0:
            print "{} was the last one.".format(self.name)

        else:
            print "There are still {:d} robots working.".format(Robot.population)

    def say_hi(self):
        print "Greetings, my master call me {}.".format(self.name)

    @classmethod
    def how_many(cls):
        print 'We have {:d} robots.'.format(cls.population)

droid1 = Robot("R2-D2") #Robot("") This constructor will call the __init__() function
droid1.say_hi()
Robot.how_many()

droid2 = Robot("C-3PO")
droid2.say_hi()
Robot.how_many()

print 'Robots can do some work here.'
print "Robots have finished their work.So let's destroy them."
droid1.die()
droid2.die()
Robot.how_many()

Recently I was reading "Concise Python Tutorial", class variables and object variables, the code in the book is shown above.

 

There are two types of fields: class variables and object variables, classified according to whether the class or object owns these variables.

There is a convention in python: the first parameter of the function is the instance object itself, and the name is named: self by default, which is equivalent to this in java.

The population property belongs to the Robot class and is a class variable.

The name variable belongs to an object (assigned by using self) and is therefore an object variable. Note: Object variables can only be defined in the constructor __init__().