8.1. JSON About¶

JavaScript Object Notation
The most popular format for data exchange

Python dict:

{"name": "Mark Watney", "age": 42, "is_astronaut": True, "friends": None}

JSON object:

{"name": "Mark Watney", "age": 42, "is_astronaut": true, "friends": null}

8.1.1. JSON or Python?¶

JSON format is similar to dict notation in Python
Fields are always enclosed only by double quote " character
Instead of True there is true (lowercase)
Instead of False there is false (lowercase)
Instead of None there is null
list is known as array (despite the same syntax)
dict is known as object (despite the same syntax)
There is no tuple or set
Coma , is not allowed after the last element in list or object
camelCase is convention, although snake_case is also valid
Unicode characters are stored as unicode entities ("cze\\u015b\\u0107")

Is the following listing a JSON object or Python list[dict]?

{'mission': 'Ares 3',
 'launch_date': datetime(2035, 6, 29),
 'destination': 'Mars',
 'destination_landing': datetime(2035, 11, 7),
 'destination_location': 'Acidalia Planitia',
 'crew': [{'name': 'Melissa Lewis', 'born': date(1995, 7, 15)},
          {'name': 'Rick Martinez', 'born': date(1996, 1, 21)},
          {'name': 'Alex Vogel', 'born': date(1994, 11, 15)},
          {'name': 'Chris Beck', 'born': date(1999, 8, 2)},
          {'name': 'Beth Johanssen', 'born': date(2006, 5, 9)},
          {'name': 'Mark Watney', 'born': date(1994, 10, 12)}]}

Is the following listing a JSON object or Python list[dict]?

{"mission": "Ares 3",
 "launch_date": "2035-06-29T00:00:00",
 "destination": "Mars",
 "destination_landing": "2035-11-07T00:00:00",
 "destination_location": "Acidalia Planitia",
 "crew": [{"name": "Melissa Lewis", "born": "1995-07-15"},
          {"name": "Rick Martinez", "born": "1996-01-21"},
          {"name": "Alex Vogel", "born": "1994-11-15"},
          {"name": "Chris Beck", "born": "1999-08-02"},
          {"name": "Beth Johanssen", "born": "2006-05-09"},
          {"name": "Mark Watney", "born": "1994-10-12"}]}

8.1.2. Pretty Printing JSON¶

JSON can be minified to save space for network transmission
It is not very readable

Minified JSON file:

$ curl https://python.astrotech.io/_static/iris.json
[{"sepalLength":5.1,"sepalWidth":3.5,"petalLength":1.4,"petalWidth":0.2,
"species":"setosa"},{"sepalLength":4.9,"sepalWidth":3,"petalLength":1.4,
"petalWidth":0.2,"species":"setosa"},{"sepalLength":4.7,"sepalWidth":3.2,
"petalLength":1.3,"petalWidth":0.2,"species":"setosa"},{"sepalLength":4.6,
"sepalWidth":3.1,"petalLength":1.5,"petalWidth":0.2,"species":"setosa"},
{"sepalLength":5,"sepalWidth":3.6,"petalLength":1.4,"petalWidth":0.2,
"species":"setosa"},{"sepalLength":5.4,"sepalWidth":3.9,"petalLength":1.7,
"petalWidth":0.4,"species":"setosa"},{"sepalLength":4.6,"sepalWidth":3.4,
"petalLength":1.4,"petalWidth":0.3,"species":"setosa"},{"sepalLength":5,
"sepalWidth":3.4,"petalLength":1.5,"petalWidth":0.2,"species":"setosa"},
{"sepalLength":4.4,"sepalWidth":2.9,"petalLength":1.4,"petalWidth":0.2,
"species":"setosa"},{"sepalLength":4.9,"sepalWidth":3.1,"petalLength":1.5,
"petalWidth":0.1,"species":"setosa"},{"sepalLength":7,"sepalWidth":3.2,
"petalLength":4.7,"petalWidth":1.4,"species":"versicolor"},
{"sepalLength":6.4,"sepalWidth":3.2,"petalLength":4.5,"petalWidth":1.5,
"species":"versicolor"},{"sepalLength":6.9,"sepalWidth":3.1,"petalLength":
4.9,"petalWidth":1.5,"species":"versicolor"},{"sepalLength":5.5,
"sepalWidth":2.3,"petalLength":4,"petalWidth":1.3,"species":"versicolor"},
{"sepalLength":6.5,"sepalWidth":2.8,"petalLength":4.6,"petalWidth":1.5,
"species":"versicolor"},{"sepalLength":5.7,"sepalWidth":2.8,"petalLength"
:4.5,"petalWidth":1.3,"species":"versicolor"},{"sepalLength":6.3,
"sepalWidth":3.3,"petalLength":4.7,"petalWidth":1.6,"species":
"versicolor"},{"sepalLength":4.9,"sepalWidth":2.4,"petalLength":3.3,
"petalWidth":1,"species":"versicolor"},{"sepalLength":6.6,"sepalWidth":2.9,
"petalLength":4.6,"petalWidth":1.3,"species":"versicolor"},{"sepalLength":
5.2,"sepalWidth":2.7,"petalLength":3.9,"petalWidth":1.4,"species":
"versicolor"},{"sepalLength":6.3,"sepalWidth":3.3,"petalLength":6,
"petalWidth":2.5,"species":"virginica"},{"sepalLength":5.8,"sepalWidth":
2.7,"petalLength":5.1,"petalWidth":1.9,"species":"virginica"},
{"sepalLength":7.1,"sepalWidth":3,"petalLength":5.9,"petalWidth":2.1,
"species":"virginica"},{"sepalLength":6.3,"sepalWidth":2.9,"petalLength":
5.6,"petalWidth":1.8,"species":"virginica"},{"sepalLength":6.5,"sepalWidth"
:3,"petalLength":5.8,"petalWidth":2.2,"species":"virginica"},{"sepalLength"
:7.6,"sepalWidth":3,"petalLength":6.6,"petalWidth":2.1,"species":
"virginica"},{"sepalLength":4.9,"sepalWidth":2.5,"petalLength":4.5,
"petalWidth":1.7,"species":"virginica"},{"sepalLength":7.3,"sepalWidth":
2.9,"petalLength":6.3,"petalWidth":1.8,"species":"virginica"},
{"sepalLength":6.7,"sepalWidth":2.5,"petalLength":5.8,"petalWidth":1.8,
"species":"virginica"},{"sepalLength":7.2,"sepalWidth":3.6,"petalLength":
6.1,"petalWidth":2.5,"species":"virginica"}]

Pretty Printing JSON:

$ curl https://python.astrotech.io/_static/iris.json |python -m json.tool
[
    {
        "petalLength": 1.4,
        "petalWidth": 0.2,
        "sepalLength": 5.1,
        "sepalWidth": 3.5,
        "species": "setosa"
    },
    {
        "petalLength": 1.4,
        "petalWidth": 0.2,
        "sepalLength": 4.9,
        "sepalWidth": 3,
        "species": "setosa"
    },
...

json.tool checks JSON syntax validity:

$ echo '{"sepalLength":5.1,"sepalWidth":3.5,}' | python -m json.tool
Expecting property name enclosed in double quotes: line 1 column 37 (char 36)

8.1.3. Use Case - 0x01¶

[
    {"firstname": "Mark", "lastname": "Watney", "missions": [
        {"year": "2035", "name": "Ares3"}]},

    {"firstname": "Melissa", "lastname": "Lewis", "missions": [
         {"year": "2030", "name": "Ares1"},
         {"year": "2035", "name": "Ares3"}]},

    {"firstname": "Rick", "lastname": "Martinez", "missions": []}
]

8.1.4. Use Case - 0x02¶

[{"firstname": "Mark", "lastname": "Watney", "addresses": [
    {"street": "2101 E NASA Pkwy", "city": "Houston", "post_code": 77058, "region": "Texas", "country": "USA"},
    {"street": "", "city": "Kennedy Space Center", "post_code": 32899, "region": "Florida", "country": "USA"}]},

 {"firstname": "Melissa", "lastname": "Lewis", "addresses": [
    {"street": "4800 Oak Grove Dr", "city": "Pasadena", "post_code": 91109, "region": "California", "country": "USA"},
    {"street": "2825 E Ave P", "city": "Palmdale", "post_code": 93550, "region": "California", "country": "USA"}]},

 {"firstname": "Rick", "lastname": "Martinez", "addresses": []},

 {"firstname": "Alex", "lastname": "Vogel", "addresses": [
    {"street": "Linder Hoehe", "city": "Cologne", "post_code": 51147, "region": "North Rhine-Westphalia", "country": "Germany"}]}]