I am trying to learn about stacks and found the following code on this website: http://interactivepython.org/runestone/static/pythonds/BasicDS/stacks.html
s = Stack()
s.push('a')
print(s.is_empty())
print(s.peek())
print(s.is_empty())
print(s.pop())
print(s.is_empty())
When running the code I get the error NameError: name 'Stack' is not defined. Can anyone help?
As per another answer,
Stack is not built-in type in Python.
So, It has to define as there is not any library stated in interactive python tutorial.
I have taken Stack() class from interactive python tutorial and your code should be like this
class Stack:
def __init__(self):
self.items = []
# I have changed method name isEmpty to is_empty
# because in your code you have used is_empty
def is_empty(self):
return self.items == []
def push(self, item):
self.items.append(item)
def pop(self):
return self.items.pop()
def peek(self):
return self.items[len(self.items)-1]
def size(self):
return len(self.items)
s = Stack()
s.push('a')
print(s.is_empty())
print(s.peek())
print(s.is_empty())
print(s.pop())
print(s.is_empty())
Output:
False
a
False
a
True
Stack is not a built-in type in python. You will need to define it first(or import from other module). In your case, you will need to run the ActiveCode 1 first.
Python lists actually behave like stacks: append() puts an item on top of the stack (it's like push() from other programming languages or other implementations, like the one you are referring to), whereas pop() can be used to retrieve the item from the top of the stack.
Stackfrom whatever module it is defined in.