current community

your communities

more stack exchange communities

company blog
Stack Exchange Inbox Reputation and Badges
tour help
Sign up ×
Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute:
up vote 1 down vote favorite
1

I want to use the variables i have declared inside a function in one class, in another class.

For example i want to use the variable "j" in another class. Is it possible? (I read somewhere that it might have something to do with instance variables but fully couldn't understand the concept).

class check1:
    def helloworld(self):
        j = 5
share|improve this question
1  
A 'function' written in this context (inside a class definition) is known as a 'method'. In python, functions are 'instance' methods, by default. An 'instance method''s first parameter (in this case, self is always an 'instance' of the class in which it is defined (for example, self is a check1 object). By doing self.j = 5, you can make the value visible to anything that has a reference to this specific self. – Darthfett Jun 1 '12 at 0:41
1  
@Darthfett You should have written that as an answer. – zigg Jun 1 '12 at 1:20
up vote 3 down vote accepted 
class check1:
    def helloworld(self):
        self.j = 5

check_instance=check1()
print (hasattr(check_instance,'j'))  #False -- j hasn't been set on check_instance yet
check_instance.helloworld()          #add j attribute to check_instance
print(check_instance.j)  #prints 5

but you don't need a method to assign a new attribute to a class instance...

check_instance.k=6  #this works just fine.

Now you can use check_instance.j (or check_instance.k) just like you would use any other variable.

This may seems a little bit like magic until you learn that:

check_instance.helloworld()

is completely equivalent to:

check1.helloworld(check_instance)

(If you think about it a little bit, that explains what the self parameter is).

I'm not completely sure what you're trying to achieve here -- There are also class variables which are shared by all instances of the class...

class Foo(object):
    #define foolist at the class level 
    #(not at the instance level as self.foolist would be defined in a method)
    foolist=[]  

A=Foo()
B=Foo()

A.foolist.append("bar")
print (B.foolist)  # ["bar"]
print (A.foolist is B.foolist) #True -- A and B are sharing the same foolist variable.
share|improve this answer
2  
I wouldnt put much effort into answering this "question". The user asking has not once accepted an answer, left a single comment, or had any other activity after posting a question... Good answer though. – chown Jun 1 '12 at 0:53
    
@chown : You're probably right, but even if the user doesn't have any activity, I can always hope that he/she will learn something from reading my post. – mgilson Jun 1 '12 at 1:01
    
@chown the fact that I didn't comment on a question means that I accepted it. although I HAVE commented to a question or two before (when I still had confusions in it). – afroze Jun 1 '12 at 7:21
    
@mgilson thanks for the solution! I can't use class variables for my particular solution. What I'm trying to achieve is have my google app engine keep working. There's i think a 30sec or so processing time out so i plan to redirect to another page in the middle of processing but i need to still access some variables from the previous page. I hope this solution works for it! (: – afroze Jun 1 '12 at 7:21
    
But I have a feeling I might not be able to use this solution since apparently when i say something like "check_instance.helloworld()" it runs the entire function/method "helloworld" (correct me if I'm wrong) and I would be essentially back to square one? (Since I obviously don't want to process the entire function/method again in the redirected page.) – afroze Jun 1 '12 at 7:30
up vote 0 down vote

j cannot be seen by another class; however, I think you meant self.j, which can.

class A(object):
    def __init__(self, x):
        self.x = x

class B(object):
    def __init__(self):
        self.sum = 0
    def addA(self, a):
        self.sum += a.x

a = A(4)
b = B()
b.addA(a)    # b.sum = 4
share|improve this answer
    
thanks got it (: – afroze Jun 1 '12 at 13:51
up vote -3 down vote

Using class inheritane it is very easy to "share" instance variables

example:

class A:
    def __init__(self):
        self.a = 10

    def retb(self):
        return self.b

class B(A):
    def __init__(self):
        A.__init__(self)
        self.b = self.a

o = B()
print o.a
print o.b
print o.retb()
share|improve this answer
2  
How does inheriting from a class allow you to share a variable defined on an instance? – mgilson Jun 1 '12 at 0:48
    
I added an example of two classes sharing each others instance variables using inheritance – voscausa Jun 1 '12 at 1:24
    
A.a is a class variable, not an instance variable. – mgilson Jun 1 '12 at 1:36
    
It is an example. But I have changed the class variable in an instance in the example. – voscausa Jun 1 '12 at 2:08

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.