You should pass the file contents (i.e. a string) to json.loads(), not the file object itself. Try this:

with open(file_path) as f:
    data = json.loads(f.read())
    print(data[0]['text'])

There's also the json.load() function which accepts a file object and does the f.read() part for you under the hood.

Use:

json.dump(standardcategories, f, indent=2)

Instead of:

json.dump(f, standardcategories, indent=2)

Notice that I've interchanged the order of f and standardcategories

json.load() is for loading a file. json.loads() works with strings.

As per the json you have shared above, the element in the list is a string. So you need to convert that into a python dict first. You can make use of python's json module for that in the following manner:

import json
feeds = []
i = 0
for feed in output['posts']:
    feed = json.loads(feed)
    feed['id'] = i
    print(feed['id'], str(feed['title']))
    i += 1
    feeds.append(feed)

You shouldn't call you're variable as json. This caused the mistake.

Do something like:

import json

not_json = open('file.json')
data = json.load(not_json)

Or even better:

with open('file.json') as input_file:
    data = json.load(input_file)

[edit]

To address to what commented below, when you declare something like:

import json

json = 2

the word json now points to a number , and you lose the name of the imported package. This is true unless you declare it in a different scope (inside a function for example).

Best practice: Try to avoid naming vars / function / classes etc in names which are built-ins, known packages etc (like: list = 2; list([1,2,3]))

fileobj is just a file object; it doesn't know that it contains JSON. Use the json library to convert it to Python data, for example:

import json

def post(postid):
    with open('used.json', 'r') as fileobj:
         data = json.load(fileobj)
    title = data[postid]
    return title

print(post(0))  # -> {'gy36v6': 'A good boy at a Minneapolis protest today'}

The file is already closed (when the previous with block finishes), so you cannot do anything more to the file. To reopen the file, create another with statement and use the read attribute to read the file.

with open('test_output.txt', 'r') as f2:
    data = f2.read()
    print(data)