Writable Attributes in python

Question

1. class Mine:
2.    def fun1(self,x):
3.        self.x=x
4.        print "Inside fun1",self.x

5.    def fun2(self):
6.        print "Inside fun2 :",self.x
7.
8.  obj1 = Mine()
9.  obj1.fun1(1)
10. obj1.fun2()

11. obj2 = Mine()
12. obj2.fun1(10000)
13. obj2.fun2()

14. del obj1.x
15. #obj1.fun2()
16. obj2.fun2()

17. Mine.a=111
18. obj3=Mine()
19. print "Mine.a: ",Mine.a
20. print "obj1.a: ",obj1.a
21. print "obj2.a: ",obj2.a
22. print "obj2.a: ",obj3.a

23. obj2.c=222
24. #print "\nMine.c: ",Mine.c
25. #print "obj1.c: ",obj1.c
26. print "obj2.c: ",obj2.c
27. #print "obj2.c: ",obj3.c

Can someone please help me to understand what is happening at line number 17 and 23, and why the code on line number 19,20,21,22 is working fine and code on line number 24, 25, 27 is giving error ?

Thanks in Advance.

hiro protagonist · Accepted Answer · 2015-09-10 20:15:10Z

1

17. Mine.a=111

you are adding a new static member a to the class Mine. the way python works (other object oriented languages do not do it this way) you can access a like it was a normal instance attribute; i.e. m = Mine(); print m.a will now work just as print Mine.a.

static members are normally added in the body of the class definition:

class Mine:
    a = 111

your second question:

23. obj2.c=222

this just adds a new member to the current instance obj2. neither the other insances of Mine nor the class Mine itself know about c.

answered Sep 10, 2015 at 20:15

hiro protagonist

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