title: How to sum numbers from a linked list?
body: <p>So for the following code I have been trying to use singly linked lists in python to calculate the sum of a list based on the even numbers within that list. I've written the code for the linked list portion I believe but I'm stumped on how to get it to actually take the even numbers only and sum them. Right now my code looks something like this:</p>
  
  <pre><code>def createList(plist):
       linkedList = None
       # goes backwards, adding each element to the beginning
       # of the list.  
       for index in range(len(plist)-1, -1, -1):
          linkedList = insertValueHead(linkedList, plist[index])
      return linkedList
  
  def sumEvens(linkedList): #This is what I'm looking for help with
      .... #code
  
  
  def testSumEvens():
      myList = createList([14, 21, 29, 2, 16, 49, -26])
      print "The sum of the even numbers in the first list is ", sumEvens(myList)
      myList = createList([])
      print "The sum of the even numbers in an empty list is ", sumEvens(myList)
      myList = createList([5, 15, 25])
      print "The sume of the even numbers in the final list is ", sumEvens(myList)
  </code></pre>
  
  <p>How would I go about making this create a sum of these lists? Such as in the first, 14 + 2 + 16?</p>