Python出错 - 试图在网页上找到更改

Question

我对我的Python代码有疑问。

我有这个代码试图通过制作一个json文件来查找网页上的更改并进行比较以查看是否每5秒钟有任何更改但我收到此错误。我认为代码中的其他所有内容都应该有效。我该如何解决这个问题？

Traceback (most recent call last):
  File "C:\Users\Admin\Desktop\binance-getmarketsalert-master\test.py", line 28, in <module>
    before_set = set([market['symbol'] for market in before['result']])
TypeError: list indices must be integers or slices, not str

代码是这样的：

import time
from smtplib import SMTPException

def build_pair_string(pairs):
    pair_string = ""
    for pair in pairs:
        pair_string += pair + "\n"

    return pair_string

while True:     
    try:
        with open('markets.json', 'r') as current_markets:
            before = json.loads(current_markets.read()) 
    except IOError:
        before = requests.get('').json()
        with open('markets.json', 'w') as current_markets:
            current_markets.write(json.dumps(before))
        print("First run... Getting initial market data.")

    after = requests.get('').json()

    new_set = after_set - before_set

    if not new_set:
        print('No changes.. Waiting 5 seconds')
        time.sleep(5)   
    if new_set:
        with open('markets.json', 'w') as current_markets:  
        duration = 500  # millisecond
        freq = 440  # Hz
        winsound.Beep(freq, duration)   
        print('Binance has added the following pairs:')
        new_list = []
        for pair in new_set:
            new_list.append(pair)  # = [item for item in pair]
        print(new_list)

        sender = 'sender@gmail.com'
        receivers = ['receiver@gmail.com']

        message = """
    Binance added {}
        """.format(build_pair_string(new_list))

        try:
            smtpObj = smtplib.SMTP_SSL('smtp.gmail.com:465')
            smtpObj.login('example@gmail.com','password')           
            print("\nSuccessfully sent email")
        except SMTPException as e:
            print(e)
            print("\nError: unable to send email")

        logging.critical('Waiting 5 seconds. New coin was listed')
        time.sleep(5)