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Parsing JSON

Almost every modern API gives you JSON. Luckily, JSON maps nicely onto normal Python data structures:

JSON objects become dicts
JSON arrays become lists

Python's built-in json.loads() can convert a JSON string:

json_string = '{"title": "The Matrix", "year": 1999}'
data = json.loads(json_string)

print(data["title"])
# The Matrix
print(data["year"])
# 1999

After that call, data is a normal Python dictionary that you can work with like any other.

Nested Data

Real JSON is usually nested. You can drill down one level at a time with bracket notation:

data = json.loads(
    '{"show": {"title": "Breaking Bad", "network": "AMC"}, "rating": {"score": 9.5}}'
)

print(data["show"]["title"])
# Breaking Bad
print(data["rating"]["score"])
# 9.5

Each pair of brackets goes one level deeper.

Missing Keys

Real API data is messy, and sometimes you try to grab a value from a key that doesn't exist:

data = {"title": "Breaking Bad"}

seasons = data["seasons"]
# raises KeyError: 'seasons'

Fortunately, the .get() let's you handle that case gracefully, it simply returns None if the key doesn't exist:

seasons = data.get("seasons")
# seasons = None

Alternatively, you can provide a default value to return instead of None:

seasons = data.get("seasons", 5)
# seasons = 5

Use bracket notation when a field must exist. Use .get() when you're not sure and a default value is acceptable.

Assignment

SnackStack's API returns device readings as JSON strings. Before the analytics team can use them, we need to parse the JSON and pull out only the fields we care about.

Complete the parse_device_reading function. It accepts a JSON string and returns a dictionary with the reading details.

Parse the JSON string with json.loads().
Return a new dictionary with these fields:
1. device_id: from the device field's id field.
2. device_type: from the device field's type field.
3. temperature: from the reading field's temperature field.
4. battery_level: from the reading field's optional battery_level field Use the .get() method so it defaults to None if the battery_level is missing.

You should print() the json_string manually to see what you're working with.