str1 = "hi hello world"

print(str1.split(" "))
输出：
['hi', 'hello', 'world']

l = ["hi","hello","world"]

print(" ".join(l))
输出：
hi hello world

class Solution:

    def isValid(self, s: str) -> bool:

        dic = {"(": ")", "{": "}", "[": "]",}

        l = []

        for i in range(len(s)):

            if s[i] in dic:#此处在字典中的是左括号！

                l.append(s[i])

            else:

                if len(l)==0:

                    return False

                elif dic[l.pop()]!=s[i]:

                    return False

        if l==[]:

            return True

        else:

            return False

class Solution:

    def isValid(self, s: str) -> bool:

        dic = {"(": ")", "{": "}", "[": "]",}

        l = []

        for i in s:

            if i in dic:

                l.append(i)

            elif len(l)==0 or dic[l.pop()]!=i:

                    return False

        return not l

class Solution:

    def isValid(self, s):

        while '{}' in s or '()' in s or '[]' in s:

            s = s.replace('{}', '')

            s = s.replace('[]', '')

            s = s.replace('()', '')

        return s == ''