Python: Return certain class variable in array from linked list

Question

Problem

I am working with class objects in a single linked list. It could be nice to have a method that returns the specific variables requested. Is this possible?

So far I am having a method under the Linked List class:

Works

class SLinkedList:
    def __init__(self):
        self.headval = None

    def getListZ(self,):
        val = self.headval
        arr = []
        while val is not None:
            arr.append(val.val.Z)
            val = val.nextval
        return arr

Wants:

class SLinkedList:
    def __init__(self):
        self.headval = None

    def getListZ(self,var):
        item = self.headval
        arr = []
        while val is not None:
            arr.append(item.val.var)
            item = item.nextval
        return arr

Questions

1. How can I write a method that returns a list of certain variables from the class objects? Let's say that I want to return a list of all the impedances. How would I do that?

Workaround

I can get a list for any desired variable (in the example, the list is called from another class):

vals1 = [item.val.val1 for item in self.list]

Iteration is possible with the following method:

    def __iter__(self):
        node = self.headval
        while node:
            yield node
            node = node.nextval

However

I would still be able to dynamically print several variables from my object in a linked list. How can I make this a variable instead of hard-coding this as I have done below?

Code

Script

class Node:
    def __init__(self, val=None):
        self.val = val
        self.nextval = None

class SLinkedList:
    def __init__(self):
        self.headval = None

    def __iter__(self):
        node = self.headval
        while node:
            yield node
            node = node.nextval

    # Function to add newnode
    def AtEnd(self, newdata):
        NewNode = Node(newdata)
        if self.headval is None:
            self.headval = NewNode
            return
        laste = self.headval
        while(laste.nextval):
            laste = laste.nextval
        laste.nextval=NewNode

    # Print the linked list
    def listprint(self,):
        printval = self.headval
        while printval is not None:
            try:
                print (printval.val.nodes,printval.val.Ctype,printval.val.Z,sep='\t')
            except:
                print (printval.val.nodes,printval.val.Ctype,sep='\t')                
            printval = printval.nextval