Explaining Code

[kozaizsvemira]

Hi,

As I am learning python I am wondering about following code:

openList = ['[', '{', '(']
closeList = [']', '}', ')']

def check(Str):
	stack = []

	for i in Str:
		if i in openList:
			stack.append(i)
		elif i in closeList:
			pos = closeList.index(i)

			if (len(stack) > 0) and (openList[pos] == stack[len(stack) -1 ]):
				stack.pop()
			else:
				print(len(stack))
				return 'Unbalanced'

	if len(stack) == 0:
		print(len(stack))
		return 'Balanced'

string = '{[()]}'
string2 = '[)'

print(string, check(string), string2, check(string2))

I understand what it does, but I've never found a full explanation of what

[] do in an example like this: openList[pos] if I understand correctly we are looking for a position and since those two lists are same length we can use it as correct position?

also this line of code:
stack[len(stack) -1 ] writing it as len(stack) - 1 returns wrong results, but what does it mean to python when we say [] I know it's a list, but how does it python see when we write list[len(list)], are we saying create another list to list len of list?