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help on object programing

class big(self):

x = 32
list = []
def inside (self):

class small(self): # a new class defined inside the first

y = 348
list.append(y) # send the value to first list

print list

how can i define my variables so that there are valid outside the

Aug 17 '07 #1
4 1132
On Aug 17, 11:07 am, yadin <conra2...@yaho o.comwrote:
class big(self):

x = 32
list = []
def inside (self):

class small(self): # a new class defined inside the first

y = 348
list.append(y) # send the value to first list

print list

how can i define my variables so that there are valid outside the

Well, first you have to create an instance of the class big:
bigInstance = big();

then to get to bigInstance's list you do bigInstance.lis t and you can
get to the list:
print bigInstance.lis t;

but the list will be empty.

check out the dive into python book to understand it object oriented
programming a little more.
Aug 17 '07 #2
On 2007-08-17, yadin <co*******@yaho o.comwrote:
class big(self):

x = 32
list = []
def inside (self):

class small(self): # a new class defined inside the first

y = 348
list.append(y) # send the value to first list

print list

how can i define my variables so that there are valid outside
the class???
Be sure to read and try the code in the sections of the Python
tutorial that discuss classes and the objects they create.

In my opinion the classes section of the official tutorial is
unfortunately the least tutorial part of the tutorial. But it
won't steer you wrong.

Neil Cerutti
Aug 17 '07 #3
how can i define my variables so that there are valid outside the
Not to be obnoxious, but your sample code has a number of fairly big
conceptual issues (like subclassing self and assigning 32 at the big
class level and printing 'list' which is a built-in type). Been there
myself - it took me a while to understand class vs. instance
variables. You are also using fairly advanced techniques such as
embedded classes which look above a newbie level.

I took the liberty to comment and "fix" up your code a bit so that it

#classes either inherit or not and signify that in parenthesis.
inheriting 'self' makes no sense
#for a class declaration. but it does make perfect sense to have
'self' as a param to a class method (def)

class big:

#class-level variable
x = 32

#changed to mylist to avoid confusion with list built-in.
mylist = []

#this is a normal instance method - 'self' refers to the class
instance you just created.
def inside (self):

#is this really what you wanted? an embedded class -
syntaxically correct, but not used often
class small: # a new class defined inside the first

y = 348
#ok, now I am referring to the mylist variable associated
(bound in python-speak) to the big class.
#y is defined here so no need to do anything
big.mylist.appe nd(y) # send the value to first list
#same with big.x
big.mylist.appe nd(big.x)
#instantiate the class, because you are calling an instance method
(i.e. you need to have created an instance to use that method)
#call the call
mybig = big().inside()

#refer to the mylist variable declared at the class, not instance
#class level means any other calls you make will alter that variable
print 'my class level mylist variable:',big. mylist

console output:

my class level mylist variable: [348, 32]

Can you perhaps rephrase your requirements to indicate what you want
to achieve?

Strictly speaking, it looks like you could do this:

class Big:
def getlist(self):
return [348,32]

mylist =Big().getlist( )

That's probably not what you were asking for, but it does express the
results you would get out of your code, especially as you are not
passing in any significant parameters to the 'inside' function.

OK, perhaps a bit more useful.

#no inheritance - could also be class Big(object) where object is the
python "root class"
class Big:

#initialize the class level to be empty
myclasslist = []
def __init__(self):
#initialize the instance level variable to be empty
self.myinstance list = []

def appendAndGet(se lf,x,y):
#modify the instance's "personal" list
self.myinstance list.append(x)
self.myinstance list.append(y)
#will now modify shared class-level variable.
Big.myclasslist .append(x)
Big.myclasslist .append(y)
return self.myinstance list
print "Big.myclasslis t without any instances around:", Big.myclasslist
bigA = Big()
result = bigA.appendAndG et(348,32)
print "result #1:", result
print "Big.myclasslis t:", Big.myclasslist

bigB = Big()
result = bigB.appendAndG et(11,22)
print "result #2:", result

#and the instance also still has its myinstancelist around
print "same as result #2:", bigB.myinstance list

print "Big.myclasslis t:", Big.myclasslist

console output:

D:\user\workspa ce\vg\tmptestin g>testc.py
my class level mylist variable: [348, 32]
Big.myclasslist without any instances around: []
result #1: [348, 32]
Big.myclasslist : [348, 32]
result #2: [11, 22]
same as result #2: [11, 22]
Big.myclasslist : [348, 32, 11, 22]

Try perhaps Dive Into Python's class intro:


Aug 17 '07 #4
yadin wrote:
class big(self):
how can i define my variables so that there are valid outside the
Although you did not describe the issue all that well, I _think_ you
are referring to the fact that the following two pieces of code behave
less like each other than one might suspect. The previous responders
have missed the confusing part of python in your attempt to present your

def big():
abc = 7
print abc
class small(object):
print '...'
print abc
def __init__(self):
print abc
return small()

class Big(object):
Abc = 13
print Abc
class Small(object):
print '...'
print Abc
def __init__(self):
print Abc
cell = Small()

The explanation is unfortunately a little technical. The
class-in-a-function (small) is not defined until the function
(big) is actually _called_, not when big is being defined. The
class-in-a-class (Small) in the second instance is actually
defined _before_ Big is being defined, and the temporary
namespace that contains Abc is hidden while Small is being

-Scott David Daniels
Sc***********@A cm.Org

Aug 18 '07 #5

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