使用python进行JSON读取：KeyError

Question

For a project to create a database, I wanted to convert .json files into .sqlite3 files using python (currently running Python 3.6.4 on Windows 10). Below is the code designed to read a json file

...

with open('C:/Documents/{}/Posts.json'.format(forum), encoding="utf8") as f:
            row = json.load(f)
            parent_id = row['_Id']
            body = format_data(row['_Body'])
            score = row['_Score']
            comment_id = row['_Id']
            comment_id_type = row['_PostTypeId']
            parent_id_type = row['_PostTypeId']
            accepted_answer_id = row['_AcceptedAnswerId']
            accepted_parent_id = row['_ParentId']

            ...

While running this code I encounter this error.

File "C:\Python\data base.py", line 85, in <module>
parent_id = row['_Id']
KeyError: '_Id'

I've read into this error finding that, according to the official python docs, the is

Raised when a mapping (dictionary) key is not found in the set of existing keys.

Now I've had trouble understanding this syntax because '_Id' exists in the json file(as seen below)

{
   "posts": {
      "row": [
         {
            "_Id": "1",
            "_PostTypeId": "1",
            "_AcceptedAnswerId": "3",
            "_CreationDate": "2016-08-02T15:39:14.947",
            "_Score": "5",
            "_ViewCount": "254",
            "_Body": "<p>What does \"backprop\" mean? I've Googled it, but it's showing backpropagation.</p>\n\n<p>Is the \"backprop\" term basically the same as \"backpropagation\" or does it have a different meaning?</p>\n",
            "_OwnerUserId": "8",
            "_LastEditorUserId": "7488",
            "_LastEditDate": "2017-05-28T13:48:02.003",
            "_LastActivityDate": "2017-05-28T13:48:02.003",
            "_Title": "What is \"backprop\"?",
            "_Tags": "<neural-networks><definitions><terminology>",
            "_AnswerCount": "3",
            "_CommentCount": "3"
         },

(This is a json from AI:stackexchange data)

I request someone help give me a solution to my KeyError, for other sources I have searched yield me no help

Please and thank you, in advance.

Answer 1

First you have to access "posts"

with open('C:/Documents/{}/Posts.json'.format(forum), encoding="utf8") as f:
    j = json.load(f)
    for row in j['posts']['row']:
        parent_id = row['_Id']
        body = format_data(row['_Body'])
        # ...

Answer 2

KeyError is raised when you request for a key which does not exist in the dictionary. In your case, from the json, it seems you have to access it like so,

json['posts' ]['row'][0].

posts is a dict. row is a list of dicts. A list is ordered, that's why we can index into it.

Full code:

with open('C:/Documents/{}/Posts.json'.format(forum), encoding="utf8") as f:
            jsondict = json.load(f)

            # Remember, posts > row > first_index
            row = jsondict['posts']['row'][0]
            parent_id = row['_Id']
            body = format_data(row['_Body'])
            score = row['_Score']
            comment_id = row['_Id']
            comment_id_type = row['_PostTypeId']
            parent_id_type = row['_PostTypeId']
            accepted_answer_id = row['_AcceptedAnswerId']
            accepted_parent_id = row['_ParentId']
            ...