Stack and queue in Python

stack = []
stack.append(1)
stack.append(2)
stack.pop()

from collections import deque
queue = deque()
queue.append(1)
queue.append(2)
queue.popleft()

def is_valid(s):
    stack = []
    pairs = {')': '(', ']': '[', '}': '{'}

    for ch in s:
        if ch in '([{':
            stack.append(ch)
        else:
            if not stack or stack.pop() != pairs[ch]:
                return False

    return not stack