TypeError: string indices must be integers with flask json

Question

I am testing a flask app where I need to post some key value pairs, but my flask app is expecting them in JSON format. At the command line I created json from my kv pairs like so:

>>> import json
>>> print json.dumps({'4': 5, '6': 7}, sort_keys=True,indent=4, separators=(',', ': '))
{
    "4": 5,
    "6": 7
}

when I put this into postman:

and post it to my app I get:

TypeError: string indices must be integers

However if I use:

[{
    "4": 5,
    "6": 7
}]

It works! Why is this happening?

Here is the app code. the error is happening at the last line:

json = request.get_json(force=True) # receives request from php
for j in json:
        print str(j)

test = [{'ad': j['4'], 'token':j['6']} for j in json]

Answer 1

You need to pass in a list of dict s because your code tries to process a list of dicts. The problem isn't related to json, that just happens to be how you read in the data structure. Here's your code as a single script demonstrating the problem. I changed the name to data to avoid confusion with json and I'm using repr instead of str to keep the problem clear.

data = {'4': 5, '6': 7}

for j in data:
        print repr(j)

test = [{'ad': j['ad'], 'token':j['token']} for j in data]

Running this results in

'4'
'6'
Traceback (most recent call last):
  File "x.py", line 6, in <module>
    test = [{'ad': j['ad'], 'token':j['token']} for j in data]
TypeError: string indices must be integers, not str

Your print statement shows that iterating through data produces strings so it makes sense that j['token'] will fail. From the looks of your code, it seems like you want to create a list of dicts from a list of dicts as input. And once you put the input dicts in a list, it ... well crashes because the dicts don't have the keys you claim... but is closer!