新对象被先前的对象覆盖

Question

I am currently trying simple python class example. I have a Parent Class (person) and a subclass (contact).

I instantiate the child class two times with different objects c1 and c2. The c2 is replacing the c1 . What am i doing wrong ?

#!/bin/python3

import time
from time import sleep

class Person (object):
    id = 0
    name = None
    fields = {}

    def __init__(self):
        ctime = time.strftime("%Y-%m-%d %H:%M:%S")
        self.fields.update({"create_time":ctime,
                            "write_time" :ctime})
        Person.id+=1

    def check_keys (self,vals):
        for k in vals:
            if not k in self.fields.keys():
                raise Exception("Key %s doesnot exists"%k)

    def update(self,*args,**kwargs):
        vals = kwargs['vals']
        self.check_keys(vals)
        self.fields.update(vals)
        ctime = time.strftime("%Y-%m-%d %H:%M:%S")
        self.fields.update({"write_time":ctime})

    def write(self,*args,**kwargs):
        vals = kwargs['vals']
        self.check_keys(vals)
        self.fields.update(vals)

    def detail (self):
        print ("Model Name is ",self.name)
        for k,v in self.fields.items():
            print("key:",k," value:",v)
        print ("#"*50)

    def get_id(self):
        return self.id

class Contact (Person):
    name="contact"
    contact_id = 0
    fields = {
        'id':None,
        'name':None,
        'age':None,
    }

c1 = Contact()
c1.update(vals={'name':'sijan','age':31,'id':c1.get_id()})
sleep(1)
c1.update(vals={'name':'sijan Shs'})

print ("calling contact 2")

c2 = Contact()
c2.update(vals={'name':'Aurelia','age':32,'id':c2.get_id()})

print ("calling contact 1")
c1.detail()
print ("calling contact 1")
c2.detail()

Here is the sample output from the last 2 c1.detail() and c2.detail()

calling contact 1
Model Name is  contact
key: id  value: 2
key: name  value: Aurelia
key: age  value: 32
key: create_time  value: 2017-03-19 15:35:54
key: write_time  value: 2017-03-19 15:35:54
##################################################
calling contact 2
Model Name is  contact
key: id  value: 2
key: name  value: Aurelia
key: age  value: 32
key: create_time  value: 2017-03-19 15:35:54
key: write_time  value: 2017-03-19 15:35:54
#################################################

I believe it should be :

calling contact 1
Model Name is  contact
key: id  value: 1
key: name  value: Sijan Shs
key: age  value: 31
key: create_time  value: 2017-03-19 15:35:53
key: write_time  value: 2017-03-19 15:35:54
##################################################
calling contact 2
Model Name is  contact
key: id  value: 2
key: name  value: Aurelia
key: age  value: 32
key: create_time  value: 2017-03-19 15:35:54
key: write_time  value: 2017-03-19 15:35:54
#################################################

I am spinning my head around trying to figure out what is going on wrong. If i use the parent class it works smooth (the behavior as predicted ie different data ). But i am having difficulty trying to understand why the subclass are behaving this way ? Am i missing some thing ?

UPDATE

What i am trying to achieve is :

I will have few more classes and each class will have their unique fields, ie forexample address for address name. How can i Achieve this without adding the field dictionary to the parent ? Example

class Address(Person):
    fields={
       'address':None
    }

Thanks a lot guys, This is working,

#!/bin/python3

import time
from time import sleep

class Person (object):
    id = 0
    name = None
    fields = {}

    def __init__(self):
        ctime = time.strftime("%Y-%m-%d %H:%M:%S")
        self.fields.update({"create_time":ctime,
                            "write_time" :ctime})
        Person.id+=1

    def check_keys (self,vals):
        for k in vals:
            if not k in self.fields.keys():
                raise Exception("Key %s doesnot exists"%k)

    def update(self,*args,**kwargs):
        vals = kwargs['vals']
        self.check_keys(vals)
        self.fields.update(vals)
        ctime = time.strftime("%Y-%m-%d %H:%M:%S")
        self.fields.update({"write_time":ctime})

    def write(self,*args,**kwargs):
        vals = kwargs['vals']
        self.check_keys(vals)
        self.fields.update(vals)

    def detail (self):
        print ("Model Name is ",self.name)
        for k,v in self.fields.items():
            print("key:",k," value:",v)
        print ("#"*50)

    def get_id(self):
        return self.id

class Contact (Person):


    def __init__(self):
        self.name="contact"
        self.fields = {
            'id':None,
            'name':None,
            'age':None
        }
        super(Contact,self).__init__()


ca = Contact()
ca.update(vals={'name':'sijan','age':31,'id':ca.get_id()})
sleep(1)
ca.update(vals={'name':'sijan Shs'})
ca.detail()

cb = Contact()
cb.detail()
cb.update(vals={'name':'Aurelia','age':32,'id':cb.get_id()})

print ("calling contact 1")
ca.detail()
print ("calling contact 2")
cb.detail()

Answer 1

This is because you are referencing class variables instead of instance variables. From the docs :

Generally speaking, instance variables are for data unique to each instance and class variables are for attributes and methods shared by all instances of the class:

 class Dog: kind = 'canine' # class variable shared by all instances def __init__(self, name): self.name = name # instance variable unique to each instance 

Instead, you could write your classes as follows:

 class Person(object):
      self.id = 0
      self.name = None
      self.fields = {}

 # rest of the class ...

 class Contact (Person):
     self.name="contact"
     self.contact_id = 0
     self.fields = {
         'id':None,
         'name':None,
         'age':None,
     }

 # rest of the class ...

Answer 2

name , id , fields are class members and so new values are not instantiated when instances of Contact which inherits from Person are made.

What you want to do is for every new instance of Contact create a new set of properties name, id, fields.

The code below does that. Pay attention to how it defines id, name, fields to be add a the instance when it is initialed ( in the __init__ function)

Since every person has name, id, fields I dont have to initiate them in the Contact class as well. See the definition of the Contact class for a cleaner implementation of the inheritance.

#!/bin/python3

import time
from time import sleep

class Person (object):
    # id = 0
    # name = None
    # fields = {}

    def __init__(self):
        self.id = 0
        self.name = None
        self.fields = {
            'id':None,
            'name':None,
            'age':None,
        }

        ctime = time.strftime("%Y-%m-%d %H:%M:%S")
        self.fields.update({"create_time":ctime,
                            "write_time" :ctime})
        self.id+=1

    def check_keys (self,vals):
        for k in vals:
            if not k in self.fields.keys():
                raise Exception("Key %s doesnot exists"%k)

    def update(self,*args,**kwargs):
        vals = kwargs['vals']
        self.check_keys(vals)
        self.fields.update(vals)
        ctime = time.strftime("%Y-%m-%d %H:%M:%S")
        self.fields.update({"write_time":ctime})

    def write(self,*args,**kwargs):
        vals = kwargs['vals']
        self.check_keys(vals)
        self.fields.update(vals)

    def detail (self):
        print ("Model Name is ",self.name)
        for k,v in self.fields.items():
            print("key:",k," value:",v)
        print ("#"*50)

    def get_id(self):
        return self.id

class Contact (Person):
    def __init__(self):
        super(Contact, self).__init__()
        self.contact_id = 0


c1 = Contact()
c1.update(vals={'name':'sijan','age':31,'id':c1.get_id()})
# sleep(1)
c1.update(vals={'name':'sijan Shs'})

print ("calling contact 2")

c2 = Contact()
c2.update(vals={'name':'Aurelia','age':32,'id':c2.get_id()})

print ("calling contact 1")
c1.detail()
print ("calling contact 1")
c2.detail()