More Python 3 ex15

aylabbs · November 27, 2017, 8:39pm

In exercise 15 (Stacks and Queues) you use the same name for the variable top and a method top of the Stack class. Is this done on purpose to get people to discover a test implementation such as:
def test_top():
stack1 = Stack()
stack1.push(‘something’)
assert Stack.top(stack1) == “something”
stack1.pop()
assert Stack.top(stack1) == None
then, realizing this probably a bad idea, rename the variable freeing up its name for the method?
Or, am I doing something wrong?

zedshaw · December 26, 2017, 9:02pm

Yes! That is a bug that is fixed in the git repository here:

github.com

zedshaw/learn-more-python-the-hard-way-solutions/blob/master/ex15_queuestack/stack.py#L29




def pop(self):
    """Pops the value that is currently on the top of the stack."""
    if self.top:
        node = self.top
        self.top = node.next
        return node.value
    else:
        return None


def first(self):
    """Returns a *reference* to the first item, does not remove."""
    return self.top != None and self.top.value or None


def count(self):
    """Counts the number of elements in the stack."""
    # same old count
    count = 0
    node = self.top
    while node:
        count += 1

I went with renaming the function from top to first.