This notebook was prepared by Donne Martin. Source and license info is on GitHub.
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%%writefile stack.py
class Node(object):
def __init__(self, data, next=None):
self.data = data
self.next = next
class Stack(object):
def __init__(self, top=None):
self.top = top
def push(self, data):
self.top = Node(data, self.top)
def pop(self):
if self.top is None:
return None
data = self.top.data
self.top = self.top.next
return data
def peek(self):
return self.top.data if self.top is not None else None
def is_empty(self):
return self.peek() is None
Overwriting stack.py
%run stack.py
%%writefile test_stack.py
import unittest
class TestStack(unittest.TestCase):
# TODO: It would be better if we had unit tests for each
# method in addition to the following end-to-end test
def test_end_to_end(self):
print('Test: Empty stack')
stack = Stack()
self.assertEqual(stack.peek(), None)
self.assertEqual(stack.pop(), None)
print('Test: One element')
top = Node(5)
stack = Stack(top)
self.assertEqual(stack.pop(), 5)
self.assertEqual(stack.peek(), None)
print('Test: More than one element')
stack = Stack()
stack.push(1)
stack.push(2)
stack.push(3)
self.assertEqual(stack.pop(), 3)
self.assertEqual(stack.peek(), 2)
self.assertEqual(stack.pop(), 2)
self.assertEqual(stack.peek(), 1)
self.assertEqual(stack.is_empty(), False)
self.assertEqual(stack.pop(), 1)
self.assertEqual(stack.peek(), None)
self.assertEqual(stack.is_empty(), True)
print('Success: test_end_to_end')
def main():
test = TestStack()
test.test_end_to_end()
if __name__ == '__main__':
main()
Overwriting test_stack.py
%run -i test_stack.py
Test: Empty stack Test: One element Test: More than one element Success: test_end_to_end
Source: https://docs.python.org/2/tutorial/datastructures.html#using-lists-as-stacks
5.1.1. Using Lists as Stacks The list methods make it very easy to use a list as a stack, where the last element added is the first element retrieved (“last-in, first-out”). To add an item to the top of the stack, use append(). To retrieve an item from the top of the stack, use pop() without an explicit index. For example: >>> stack = [3, 4, 5] >>> stack.append(6) >>> stack.append(7) >>> stack [3, 4, 5, 6, 7] >>> stack.pop() 7 >>> stack [3, 4, 5, 6] >>> stack.pop() 6 >>> stack.pop() 5 >>> stack [3, 4]