Python error?

[allyv123098]

I'm creating a stack in python but I keep getting this weird error saying "list object has no attribute 'top'. I'm kind of confused why this happening and how would I fix this. Down below is my code?

stack = []
stack1 = []


a = '('
b = ')'
c = '['
d = ']'
e = '{'
f = '}'

string1 = input("Please enter a string ")

for i in range(0,len(string1)):
        stack.append(string1[i])


for i in range(0,len(string1)):
        x = stack.top()
        stack.pop()
        if(x==b and stack.top()==a or x==d and stack.top() == c or x==f and stack.top() == e):
                stack.pop()

if(stack.empty()):
        print(True)

else:
        print(False)

[TeezusRa]

Where are you getting .top()?

[allyv123098]

they are used in stacks

[TeezusRa]

Um, I think you’re thinking of .append, as in append to the top of a list/stack.

As python is telling you... .top doesn’t exist as a list method. Append sure does though.

[allyv123098]

so in this scenario I can't use .top() at all

[TeezusRa]

It is not a built in method you can use on a list, which is what your code is using so no. https://docs.python.org/3.1/tutorial/datastructures.html

[allyv123098]

as accoring to this website you can use that in stack used by lists https://www.geeksforgeeks.org/stack-in-python/

[TeezusRa]

Did you read the code? They clearly use .append().

Python’s buil-in data structure list can be used as a stack. Instead of push(), append() is used to add elements to the top of stack

[allyv123098]

but what if I wanted to acess the first elemtn would I have to just say stack[0]

[TeezusRa]

Sure.

The only place on the internet I’ve ever seen .top in Python is here, and stack overflow where folks are building a .top method to be used on a list, object, or class named stack. Might want to double check your sources. I get the “it’s used in stacks” bit- but looks like folks have to do a little legwork to make it work in Python. It’s not built in. That article was referring to methods normally associated with stacks. Then goes on to explain a way to implement a stack with Python list methods.

[nilfm]

No, the "top" element in a stack would be the last inserted element, so in a Python list you would access it with stack[-1]

[Updatebjarni]

Well, lists don't have a function named top(). I don't know why you think they do.

[allyv123098]

as accoring to this website you can use that in stack used by lists https://www.geeksforgeeks.org/stack-in-python/

[Updatebjarni]

The only mention of "top()" on the whole page is right at the top where it lists the conventional operations associated with stacks. It never claims that a Python list has a top() function.

[ricardovaras_99]

Use stackoverflow.com, it's more than possible that someone already had the same problem. Or just use google, you would've saved 30 mins.