def pop(self):
if self.top:
val = self.top.value
self.top = self.top.next
return val
else:
raise InvalidOperationError(
"Method not allowed on empty collection")
def dequeue(self):
if self.front:
temp = self.front
self.front = self.front.next
temp.next = None
return temp.value
else:
raise InvalidOperationError(
"Method not allowed on empty collection")
def peek(self):
if self.front:
return self.front.value
else:
raise InvalidOperationError(
"Method not allowed on empty collection")