TypeError：字符串索引必须是整数。 Python，烧瓶[关闭]

Question

我有一个通过 Flask 中的会话创建的简单购物车：

session['cart'] += [{
    'product_name': request.form['product_name'],
    'product_cost': request.form['product_cost'],
    'product_img': request.form['product_img'],
}]

购物车示例：

product_cart = [{'product_name': 'product1', 'product_cost': '300', 'product_img': ''},
                {'product_name': 'product2', 'product_cost': '400', 'product_img': ''},
                {'product_name': 'product3', 'product_cost': '300', 'product_img': ''},
               ]

在哪里product_cart = session['cart']

我需要得到product_cost 值的总和。我试图这样做：

sum([int(product['product_cost']) for product in product_cart ])

但是出现了这个错误：TypeError: string indices must be integers。正如我未测试的那样，product_cost 应该是 int 类型，而不是 dict 中的 str。但是当我尝试获取它们的总和时，我已经将其转换为int（请参阅更高的代码）。

那么，我做错了什么，我该如何解决这个错误？谢谢！

编辑：

print(session['cart']:

[{'product_name': 'product1', 'product_cost': '300', 'product_img': '*binary img*'}, {'product_name': 'product2', 'product_cost': '400', 'product_img': '*binary img*'}]

完整追溯：

Traceback (most recent call last):
    File "C:\Users\User\AppData\Local\Programs\Python\Python39\Lib\site-packages\flask\app.py", line 2464, in __call__
return self.wsgi_app(environ, start_response)
  File "C:\Users\User\AppData\Local\Programs\Python\Python39\Lib\site-   packages\flask\app.py", line 2450, in wsgi_app
response = self.handle_exception(e)
  File "C:\Users\User\AppData\Local\Programs\Python\Python39\Lib\site-packages\flask\app.py", line 1867, in handle_exception
reraise(exc_type, exc_value, tb)
  File "C:\Users\User\AppData\Local\Programs\Python\Python39\Lib\site-packages\flask\_compat.py", line 39, in reraise
raise value
  File "C:\Users\User\AppData\Local\Programs\Python\Python39\Lib\site-packages\flask\app.py", line 2447, in wsgi_app
response = self.full_dispatch_request()
  File "C:\Users\User\AppData\Local\Programs\Python\Python39\Lib\site-packages\flask\app.py", line 1952, in full_dispatch_request
rv = self.handle_user_exception(e)
  File "C:\Users\User\AppData\Local\Programs\Python\Python39\Lib\site-packages\flask\app.py", line 1821, in handle_user_exception
reraise(exc_type, exc_value, tb)
  File "C:\Users\User\AppData\Local\Programs\Python\Python39\Lib\site-packages\flask\_compat.py", line 39, in reraise
raise value
  File "C:\Users\User\AppData\Local\Programs\Python\Python39\Lib\site-packages\flask\app.py", line 1950, in full_dispatch_request
rv = self.dispatch_request()
  File "C:\Users\User\AppData\Local\Programs\Python\Python39\Lib\site-packages\flask\app.py", line 1936, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
  File "C:\Users\User\Documents\Projects\jewelry-store\app.py", line 336, in cart
full_cost = sum([int(product['product_cost']) for product in cart_products ])
  File "C:\Users\User\Documents\Projects\jewelry-store\app.py", line 336, in <listcomp>
full_cost = sum([int(product['product_cost']) for product in cart_products ])
TypeError: string indices must be integers

Answer 1

这里有些东西没有加起来（没有双关语）：

full_cost = sum([int(product['product_cost']) for product in cart_products ])
TypeError: string indices must be integers

当您问题中的 product_cart 作为输入提供时，它应该可以工作。

但是，如果您有一个字符串作为 product_cart 列表的成员，而不是字典，则会抛出此异常：

>>> product_cart = ['test']
>>> sum([int(product['product_cost']) for product in product_cart ])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 1, in <listcomp>
TypeError: string indices must be integers

或者换一种说法：

>>> {'product_cost':'123'}['product_cost']
'123'
>>> 'some_string'['product_cost']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: string indices must be integers

因此，您在代码中看到的异常是因为 sum 函数中的列表理解正在获取 product 的字符串。

您的session['cart'] 中似乎有些问题，因此任何人都无法使用此问题中提供的信息来解决问题，抱歉。