FAQ: Learn Python: Files - Writing a JSON File

This community-built FAQ covers the “Writing a JSON File” exercise from the lesson “Learn Python: Files”.

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This exercise can be found in the following Codecademy content:

Learn Python 3

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How do we append new data into an existing JSON file? Do we simply open the file with “a” mode, and calling the function json.dump()?


In this lesson, data_payload is a dictionary wrapped in [] - a list of a dictionary. Isn’t JSON like an object and uses just {}?

So, we make a JSON file out of a dictionary in a list…what if we wanted to further convert this list to an actual dictionary? I tried

import json
with open('data.json') as data_json:
  data = json.load(data_json)

#Expected result: 
>>{'interesting message': 'What is JSON? A web application\'s little pile of secrets.',
   'follow up': 'But enough talk!'}
#Actual result:
>>> {'interesting message': 'follow up'}

I am curious about this as well, if anybody here has some experience with that type of appending?

Hey guys! My question is actually about the next project, the medical data project linked at the bottom. I didn’t know the best forum to post a question, so I backed up to here.

Good Day! I am Laura and am trying to learn data science to make a career change. I do not have previous tech experience other than working through some MDN courses on HTML and javascript, as well as ~15% of the Full-Stack program through codacademy. I am at the Medical Data group project and am really stuck. Right off the bat, I am having trouble understanding how to import my CSV file.
Can someone explain? Thank you! Below is my initial code and the error. Help!

import csv
ages =
sexes =
bmis =
num_children =
smoker_statuses =
regions =
insurance_charges =
def create_list(lst, csv_file, column_name):
with open(“C:\Users\florence\Documents\python-portfolio-project-starter-files\insurance.csv”) as csv_info:
csv_dict = csv.DictReader(csv_info)
for row in csv_dict:
return lst

The error returned:
File “C:\Users\florence\AppData\Local\Temp/ipykernel_16848/3400907934.py”, line 2
with open(“C:\Users\florence\Documents\python-portfolio-project-starter-files\insurance.csv”) as csv_info:
SyntaxError: (unicode error) ‘unicodeescape’ codec can’t decode bytes in position 2-3: truncated \UXXXXXXXX escape

Below is a link to the project I am referring to:
Group Project: U.S. Medical Insurance Costs | Codecademy

In a normal string Python uses the backslash \ as an escape character so it will be interpreted in an unexpected way in your code (if you’re unsure try just using that string to assign to a variable or print and I think you’ll get the same error, I don’t think it’s from the file itself).

You can either use a forward slash / and Python will interpret the path for you, you can escape each backslash with another backslash, e.g. C:\\Users\\name\\ or you can make the string itself a “raw-string” which no longer interprets the backslash as a special escape character. For a raw string put r before the string, e.g. r"raw\string with a \ is OK".

If that hasn’t covered the issue I think #get-help might be the best shout with #project as another option (shorter queries in get-help, general discussion of the project itself in projects). If you’re posting code to the forums have a look at- How do I format code in my posts? as it contains details of how to retain indentation and format the code which makes it much easier to read :slightly_smiling_face:.

thank you for your tips. I think I’m more stuck then I thought because it doesn’t even seem to recognize my having imported csv, as it says this is not defined… I’ll try to find a better forum to ask…

I too am curious why data_payload has both square brackets, and curly braces

data_payload = [
  {'interesting message': 'What is JSON? A web application\'s little pile of secrets.',
   'follow up': 'But enough talk!'}

I was trying to access the data inside of data.json file:

data_payload = [
  {'interesting message': 'What is JSON? A web application\'s little pile of secrets.',
   'follow up': 'But enough talk!'}

import json

with open('data.json', 'w') as data_json:
  json.dump(data_payload, data_json)

with open('data.json') as data_json:
  data = json.load(data_json)
  print(data['interesting message'])

… but I got a error

Traceback (most recent call last):
  File "script.py", line 13, in <module>
    print(data['interesting message'])
TypeError: list indices must be integers or slices, not str```

Someone have the idea how to access this data?

I think this json creates a list containing a dictionary (from the json.load() ), just like the data_payload.

with open('data.json') as data_json:
  data = json.load(data_json)
  for entry in data:
    for key, value in entry.items():
      print("{}: {}".format(key, value))
1 Like

I had the same doubt. Then I realized what we ‘dumped’ to the json file was a list (containing a dictionary), that’s why we had to access it with an INT, like @janbazant1107978602 proposed