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[Program Query]Classes and Methods

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Join Date: Mar 2008

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mcenley

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[Program Query]Classes and Methods

Apr 2nd, 2008

Hi friends,
My problem definition is as follows:
Creating a class name called "Kangaroo".
1] An __init__ method that initializes an attribute named pouch_contents to an empty list.
2]A method named by creating put_in_pouch that takes an object of any type and adds it to pouch_contents.

The following is the code I have written:

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
class Kangaroo:
    def __init__(self,pouch=[],pouch_contents=10):
        self.pouch.append(pouch_contents)
        print self.pouch
 
 
    def __add__(self,other):
        if isinstance(other,Kangaroo):
            return self.put_in_pouch(other)
        else:
            return False
 
    def __print__(self):
        print '%d'% (self.pouch)
 
 
    def put_in_pouch(self,other):
        temp=Kangaroo()
        temp.pouch=self.pouch+other.pouch
        return temp
 
 
 
kanga=Kangaroo()
roo=Kangaroo()
print kanga + roo
class Kangaroo:
    def __init__(self,pouch=[],pouch_contents=10):
        self.pouch.append(pouch_contents)
        print self.pouch
        
        
    def __add__(self,other):
        if isinstance(other,Kangaroo):
            return self.put_in_pouch(other)
        else:
            return False
        
    def __print__(self):
        print '%d'% (self.pouch)

        
    def put_in_pouch(self,other):
        temp=Kangaroo()
        temp.pouch=self.pouch+other.pouch
        return temp

    

kanga=Kangaroo()
roo=Kangaroo()
print kanga + roo

I am testing the code by creating 2 Kangaroo class objects. But for the surprising fact that the pouch_contents don't get added to the specific Kangaroo object. It adds to a normal list. But it's not what I want. I want to add the pouch_contents for the specific object as it I ultimately would like to add contents off 2 different objects.

Kindly help.

Thank You.

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Join Date: Aug 2005

Location: England - York

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a1eio

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Re: [Program Query]Classes and Methods

Apr 2nd, 2008

not sure what you mean exactly, but why are you creating a temporary instance of Kangaroo in the put in pouch function?
I thought you meant you wanted roo's pouch added into kanga's pouch?

if thats the case then your code is fine, except you need to define pouch in init.

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
class Kangaroo:
    def __init__(self, contents=10):
        self.pouch = []
        self.pouch.append(contents)
...
...
...
    def put_in_pouch(self, other)
        self.pouch.extend(other.pouch)
 
master = Kangaroo('master')
for i in range(10):
    master + Kangaroo(i)
 
print master.pouch
class Kangaroo:
    def __init__(self, contents=10):
        self.pouch = []
        self.pouch.append(contents)
...
...
...
    def put_in_pouch(self, other)
        self.pouch.extend(other.pouch)

master = Kangaroo('master')
for i in range(10):
    master + Kangaroo(i)

print master.pouch

my result is:

Help with Code Tags

(Toggle Plain Text)

>>> 
['master']
[0]
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
['master', 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>>

hope that helps
a1eio

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mcenley

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Re: [Program Query]Classes and Methods

Apr 2nd, 2008

Hi,
Firstly, Thank You.
Secondly,
I have now modified my code :

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
class Kangaroo:
    def __init__(self,pouch_contents=10):
        self.pouch=[]
        self.pouch.append(pouch_contents)
        print self.pouch
 
 
    def __add__(self,other):
        if isinstance(other,Kangaroo):
            return self.put_in_pouch(other)
        else:
            return False
 
    def __str__(self):
        print self.pouch
 
 
    def put_in_pouch(self,other):
        self.pouch.extend(other.pouch)
        return self
 
 
 
kanga=Kangaroo()
roo=Kangaroo(100)
kanga + roo
print kanga.pouch
class Kangaroo:
    def __init__(self,pouch_contents=10):
        self.pouch=[]
        self.pouch.append(pouch_contents)
        print self.pouch
        
        
    def __add__(self,other):
        if isinstance(other,Kangaroo):
            return self.put_in_pouch(other)
        else:
            return False
        
    def __str__(self):
        print self.pouch

        
    def put_in_pouch(self,other):
        self.pouch.extend(other.pouch)
        return self

    

kanga=Kangaroo()
roo=Kangaroo(100)
kanga + roo
print kanga.pouch

I would like to take advantage of the __str___ function.
However, whenever I say print kanga + roo it doesn't gives me an error as to __str__ is returning a non-string type.
I usually use the __str__ special method to print my data directly.

What could probably be the problem?

PS: I am learning Python and hence the mistakes I make are obvious.Sorry !

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Join Date: Aug 2005

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a1eio

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Junior Poster

Re: [Program Query]Classes and Methods

Apr 2nd, 2008

well, if you want to be able to 'print' the kangaroo instance in your case your trying to print 'kanga' then just make the '__str__' method return a string and that string will get printed:

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
...
...
    def __str__(self):
        return str(self.pouch)
....
....
kanga = Kangaroo()
roo = Kangaroo()
kanga + roo
print kanga
...
...
    def __str__(self):
        return str(self.pouch)
....
....
kanga = Kangaroo()
roo = Kangaroo()
kanga + roo
print kanga

i get:

Help with Code Tags

(Toggle Plain Text)

>>> 
[10]
[100]
[10, 100]
>>>

hope that helps
a1eio

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mcenley

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Re: [Program Query]Classes and Methods

Apr 2nd, 2008

Hi,
Is there any other method to which a list can be returned ?

__str__ is for String is there a special method for lists ?

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a1eio

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Junior Poster

Re: [Program Query]Classes and Methods

Apr 2nd, 2008

i'm not sure, i havn't used the double underscore methods much (if at all) but as far as i am aware, the __str__ method links with the 'print' keyword, so if print object is called then that objects __str__ method would be called and the result (returned value) of that would be displayed if it was a string, otherwise it returns an error.
So i'm not really sure if there's a method to return a list.

I am currently looking through the following page to see what kinda things you can do. You will probably find it useful also, although sometimes the documentation is a bit hard to understand (i think so anyway).

hope that helps
a1eio

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mcenley

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Re: [Program Query]Classes and Methods

Apr 2nd, 2008

•

Originally Posted by a1eio

i'm not sure, i havn't used the double underscore methods much (if at all) but as far as i am aware, the __str__ method links with the 'print' keyword, so if print object is called then that objects __str__ method would be called and the result (returned value) of that would be displayed if it was a string, otherwise it returns an error.
So i'm not really sure if there's a method to return a list.

I am currently looking through the following page to see what kinda things you can do. You will probably find it useful also, although sometimes the documentation is a bit hard to understand (i think so anyway).

hope that helps
a1eio

Oh yes, about the __str__ method you are right, it does link with print. I was probably asking for a bit more from the method.
By the way,Which page are you looking at ?