JSON (JavaScript Object Notation) is a way of writing data as text. It looks almost exactly like Python dictionaries and lists, and it's how most programs and websites exchange data: when an app fetches the weather, the reply is usually JSON.

{"city": "Canterbury", "temp": 14.5, "rain": true, "days": ["Mon", "Tue"]}

The json module converts in both directions:

import json

text = '{"city": "Canterbury", "temp": 14.5, "rain": true, "days": ["Mon", "Tue"], "alert": null}'
data = json.loads(text)
print(type(data), data["temp"], data["days"][1])
print(data)

back = json.dumps(data)
print(back)
print(json.dumps(data, indent=2))

json.loads(text) ("load string") turns JSON text into Python data.
json.dumps(data) ("dump string") turns Python data into JSON text. indent=2 makes it readable.

JSON	Python
object `{}`	dict
array `[]`	list
string	str
number	int or float
`true` / `false`	`True` / `False`
`null`	`None`

JSON keys must be strings in double quotes, and there are no tuples or sets: they come back as lists.