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Scope of a class..help???

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  Scope of a class..help??? lokeshkoppaka@gmail.com - 2013-05-23 02:51 -0700
    Re: Scope of a class..help??? Chris Angelico <rosuav@gmail.com> - 2013-05-23 20:00 +1000
    Re: Scope of a class..help??? Peter Otten <__peter__@web.de> - 2013-05-23 12:18 +0200
    Re: Scope of a class..help??? lokeshkoppaka@gmail.com - 2013-05-23 03:23 -0700
      Re: Scope of a class..help??? Chris Angelico <rosuav@gmail.com> - 2013-05-23 20:27 +1000
    Re: Scope of a class..help??? lokeshkoppaka@gmail.com - 2013-05-23 03:25 -0700
      Re: Scope of a class..help??? Chris Angelico <rosuav@gmail.com> - 2013-05-23 21:40 +1000
      Re: Scope of a class..help??? Tim Roberts <timr@probo.com> - 2013-05-23 22:05 -0700

#45786 — Scope of a class..help???

i had written the following code i am unable to create the instance of the class "Node" in the method "number_to_LinkedList" can any one help me how to do ??
and what is the error??
  

class Node:
    def __init__(self, value=None):
        self.value = value
        self.next = None



def number_to_LinkedList(numbers):
      pass
      list_numbers = list(numbers)
      head_node = Node() #unable to create the instance saying UnboundedLocal
      head_node.value = list_numbers[0]
      head_node.next = None
      current_node = head_node
      for i in range(1,len(list_numbers)):
        new_node = Node()
        new_node.value = list_numbers[i]
        new_node.next = current_node
        current_node = new_node
      current_node.next = None
      while Node:
        print Node.data
        Node = Node.next

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#45790

On Thu, May 23, 2013 at 7:51 PM,  <lokeshkoppaka@gmail.com> wrote:
> i had written the following code i am unable to create the instance of the class "Node" in the method "number_to_LinkedList" can any one help me how to do ??
> and what is the error??

It would really help if you post the actual exception and traceback.
It's UnboundLocal, not Unbounded... and here's the problem:

> def number_to_LinkedList(numbers):
>       head_node = Node() #unable to create the instance saying UnboundedLocal
>       while Node:
>         print Node.data
>         Node = Node.next

You're assigning to Node. I think you mean to have some other local
variable here, for the iteration at the end. Since you assign to the
name Node inside the function (and don't have a global declaration),
the name Node is local to the function. Python doesn't let you
reference the global "prior to" shadowing it with the local, so you
get this error.

ChrisA

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#45791

lokeshkoppaka@gmail.com wrote:

> i had written the following code i am unable to create the instance of the
> class "Node" in the method "number_to_LinkedList" can any one help me how
> to do ?? and what is the error??
>   
> 
> class Node:
>     def __init__(self, value=None):
>         self.value = value
>         self.next = None
> 
> 
> 
> def number_to_LinkedList(numbers):
>       pass
>       list_numbers = list(numbers)
>       head_node = Node() #unable to create the instance saying
>       UnboundedLocal head_node.value = list_numbers[0]
>       head_node.next = None
>       current_node = head_node
>       for i in range(1,len(list_numbers)):
>         new_node = Node()
>         new_node.value = list_numbers[i]
>         new_node.next = current_node
>         current_node = new_node
>       current_node.next = None
>       while Node:
>         print Node.data
>         Node = Node.next

You have to decide if you want to use a name in a function locally or to 
access a global. Python treats names that are being assigned to anywhere in 
a function as local throughout the whole function.

x = "global"
def f():
    print x # ok, access global variable

x = "global"
def g():
    x = "local"
    print x # ok, accessing local variable

x = "global"
def h():
    print x # error, accessing local variable that has not 
            # been assigned a value
    x = "local"

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#45792

 Thanks Chris Angelico,
i am new to python can you suggest me how to remove the error and solve it.
so,how can i create an instance for "Node" in that function??,is, it not possible to create an instance in such a way?

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#45794

On Thu, May 23, 2013 at 8:23 PM,  <lokeshkoppaka@gmail.com> wrote:
>  Thanks Chris Angelico,
> i am new to python can you suggest me how to remove the error and solve it.
> so,how can i create an instance for "Node" in that function??,is, it not possible to create an instance in such a way?

The problem isn't the instantiation; the problem's further down, where
you reuse the name "Node" to iterate over your list. Rename that to
something else and you should be right.

ChrisA

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#45793

ok Peter Otten,
but how to make a Class global??

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#45801

On Thu, May 23, 2013 at 8:25 PM,  <lokeshkoppaka@gmail.com> wrote:
> ok Peter Otten,
> but how to make a Class global??

He gave some examples. It'd be helpful to quote some of his post, for
context... and preferably, show some proof that you've understood it.

You're starting a number of threads that look like you're trying to
get us to do your homework. You need to demonstrate that you actually
understand the material you're supposed to be learning.

ChrisA

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#45866

lokeshkoppaka@gmail.com wrote:
>
>ok Peter Otten,
>but how to make a Class global??

Your class IS global.  I still don't think you understand what you did
wrong.  You've tripped into a strange little quirk of scoping.  Here is
your code with some unimportant lines removes.

class Node:
    def __init__(self, value=None):
        self.value = value
        self.next = None

## OK, at this point, you have a global called "Node", which is a class.

def number_to_LinkedList(numbers):
      pass
      list_numbers = list(numbers)
      head_node = Node()
      # ... 
      current_node.next = None
      while Node:
        print Node.data

Python actually does a first scan through your function before it starts to
compile it.  When it does the scan, it sees you use the name "Node" as a
local variable.  At that point, it remembers that "in this function scope,
'Node' is a local name".  Now, it codes to compile the class.  When it
encounters Node() for the first time, it sees that "Node" is not defined
locally, even though it was supposed to be a local name.

You are assuming that the first Node() in that function will automatically
refer to the global class.  It won't.  The only way to solve this dilemma
is to change the name you use in the "while" loop.
-- 
Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.

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