Is there a way to catch this unexpected value-CodePudding

[(9, '['), (25, ']'), (442, '['), (460, ']'), (558, '['), (576, ']'), (608, ']')]

In this list of tuples I am trying to find key of "]" in the end. If you take a closer look values goes like this;

[ => ] => [ => ] => [ => ] => [ => ]

But at last step it goes;

] => ]

I want to find key when this unexpected value appear. How can I do that?

CodePudding user response：

This is a typical matching brackets exercise that is easily solved using the concept of a stack.

from collections import deque

brackets = {"[": "]"}
stack = deque()

for item in data:
    val, bracket = item
    if bracket in brackets:
        stack.append(bracket)
    else:
        try:
            openb = stack.pop()
        except IndexError:
            print(val)
        if brackets[openb] != bracket:
            print(val)

>> 608

CodePudding user response：

I think you're looking for something like this:

from itertools import cycle

L = [(9, '['), (25, ']'), (442, '['), (460, ']'), (558, '['), (576, ']'), (608, ']')]
c = cycle(['[', ']'])

for t in L:
    if t[1] != next(c):
        print(t[0])
        break