b = contents['comments'] TypeError: string indices must be integers

This error occurs when we try to use a string as an index for accessing elements in a dictionary.

For example, if we have a dictionary like this:

my_dict = {'name': 'John', 'age': 25, 'gender': 'male'}

We can access the value of the 'name' key using the index notation like this:

name = my_dict['name']

However, if we try to use a string as an index, we will get a TypeError. For example:

my_dict['John']  # TypeError: string indices must be integers

In the given code, the variable contents seems to be a string, not a dictionary. Therefore, we cannot access its elements using the index notation. To fix this error, we need to convert the string to a dictionary first. We can do this using the `json.loads()` function, which parses a JSON string and returns a dictionary:

import json

contents = '{"comments": [{"id": 1, "text": "Great post!"}, {"id": 2, "text": "Thanks for sharing."}]}'  # example string
data = json.loads(contents)   # convert string to dictionary
comments = data['comments']   # access the 'comments' key

Now we can access the 'comments' key without getting a TypeError.