def test_peek():
stack = Stack()
stack.push('Dwight')
stack.push('Michael')
stack.push('Jim')
stack.push('Andy')
stack.peek()
actual = stack.top.value
expected = 'Andy'
assert actual == expected
def test_peek_one():
s = Stack()
s.push("apple")
s.push("banana")
actual = s.peek()
expected = "banana"
assert actual == expected
class PsuedoQueue:
"""
This is a queue being implement using stack's
push, pop and peek methods rather than having
its own attributes and methods
"""
def __init__(self):
self.front_stack = Stack()
self.rear_stack = Stack()
# this is strictly here so that we may pass a test,
self.front = None
def peek(self):
return self.front_stack.peek()
def is_empty(self):
return self.front_stack.is_empty()
def enqueue(self, value=None):
node = Node(value)
if self.rear_stack.top:
self.rear_stack.top.next = node
self.rear_stack.top = node
if not self.front_stack.top:
self.front_stack.top = node
# next line is solely here to pass a test
self.front = self.front_stack.top
def dequeue(self):
# if the queue only holds one node, we must manually set the rear to None
if (self.rear_stack.top == self.front_stack.top):
self.rear_stack.top = None
value = self.front_stack.pop()
# next line is solely here to pass a test
self.front = self.front_stack.top
return value
def test_peek_empty():
s = Stack()
with pytest.raises(InvalidOperationError) as e:
s.peek()
assert str(e.value) == "Method not allowed on empty collection"
def test_peek():
s = Stack()
s.push("apple")
actual = s.peek()
expected = "apple"
assert actual == expected
def test_peek_on_empty():
new_stack = Stack()
with pytest.raises(InvalidOperationError) as e:
new_stack.peek()
