Christopher Spears wrote: > I am working out of How To Think Like A Computer > Scientist. Here is the code for a module called > node.py: > > def printList(node): > nodeList = [] > while node: > nodeList.append(node.cargo) > node = node.next > print nodeList > > def printBackward(node): > if node == None: return > head = node > tail = node.next > printBackward(tail) > print head, > > class Node: > def __init__(self, cargo=None, next=None): > self.cargo = cargo > self.next = next > > def __str__(self): > return str(self.cargo) > > > I'm trying to figure out how the printBackward > function works. I understand it moves up a linked > list until it reaches the end of the list. Why does > it print every node? Shouldn't it just print the last > one? printBackward() scans to the end of the list by making nested calls to itself. Each call is matched by a return which returns to the place where it was in the next call up the stack. So the most deeply nested call will print head and return to the next-most-deeply-nested call which will print head, etc.
Each call has its own set of local variables (called a stack frame) - its own value for node, head and tail. So the print statements print all the cargo in the list. We just had a discussion of recursion, you might want to look at it - though the code is a bit more complex than this example. http://mail.python.org/pipermail/tutor/2006-July/048081.html Kent _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
