4.15.py

class NestedInteger(object):
    def __init__(self, value=None):
       """
       If value is not specified, initializes an empty list.
       Otherwise initializes a single integer equal to value.
       """
    def __call__(self, a):
        return a 

class Solution:
    def deserialize(self, s: str) -> NestedInteger:
        index = 0

        def dfs() -> NestedInteger:
            nonlocal index
            if s[index] == '[':
                index += 1
                ni = NestedInteger()
                while s[index] != ']':
                    ni.add(dfs())
                    if s[index] == ',':
                        index += 1
                index += 1
                return ni
            else:
                negative = False
                if s[index] == '-':
                    negative = True
                    index += 1
                num = 0
                while index < len(s) and s[index].isdigit():
                    num *= 10
                    num += int(s[index])
                    index += 1
                if negative:
                    num = -num
                return NestedInteger(num)

        return dfs()

a = Solution()
b = a.deserialize('324')
print(b(1))