Variables versus name bindings [Re: A certainl part of an if() structure never gets executed.]

[Roel Schroeven]

Νίκος schreef:
> Στις 18/6/2013 12:05 μμ, ο/η Steven D'Aprano έγραψε:
>> Names are *always* linked to objects, not to other names.
>>
>> a = []
>> b = a  # Now a and b refer to the same list
>> a = {} # Now a refers to a dict, and b refers to the same list as before
> 
> I see, thank you Steven.
> 
> But since this is a fact how do you create complicated data structures 
> that rely on various variables pointing one to another liek we did in 
> C++(cannot recall their names) ?

You almost never need to do that in Python. But if you really want to, 
out of curiosity, you can. For example, you could create a simple singly 
linked list like this:

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

		
 >>> first = Node(1)
 >>> second = Node(2)
 >>> first.next = second

You could iterate over it like this:

 >>> def iterate_linked_list(node):
	while node:
		yield node.value
		node = node.next

		
 >>> for v in iterate_linked_list(first):
	print v


-- 
"People almost invariably arrive at their beliefs not on the basis of
proof but on the basis of what they find attractive."
         -- Pascal Blaise

roel at roelschroeven.net