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What is JSON?

JSON is just a (usually long) string whose contents follow a specific format.

One example of JSON:

"key": "value",
"another": 25,
"listic_data": [
"sub_objects": {
"name": "Rolf",
"age": 25

So at its core, you've got:

  • Strings
  • Numbers
  • Booleans (true or false)
  • Lists
  • Objects (akin to dictionaries in Python)
    • Note that objects are not ordered, so the keys could come back in any order. This is not a problem!

At the top level of a piece of JSON you can have an object or a list. So this is also valid JSON:

"name": "Rolf",
"age": 25
"name": "Anne",
"age": 27
"name": "Adam",
"age": 23

When we return a Python dictionary in a Flask route, Flask automatically turns it into JSON for us, so we don't have to.

Remember that "turning it into JSON" means two things:

  1. Change Python keywords and values so they match the JSON standard (e.g. True to true).
  2. Turn the whole thing into a single string that our API can return.

Note that JSON can be "prettified" (as the above examples), although usually it is returned by our API "not-prettified":


This removal of newlines and spaces, believe it or not, adds up and can save a lot of bandwidth since there is less data to transfer between the API server and the client.