16.1. JSON About

JavaScript Object Notation
The most popular format for data exchange
JSON format is similar to dict notation in Python

Python dict:

{
    'firstname': 'Alice',
    'lastname': 'Apricot',
    'height': 170,
    'weight': 55.5,
    'is_staff': True,
    'is_admin': False,
    'friends': None,
    'groups': ('users', 'staff'),
    'project': {'id': 1, 'name': 'myproject'}
}

JSON object:

{
    "firstname": "Alice",
    "lastname": "Apricot",
    "height": 170,
    "weight": 55.5,
    "isStaff": true,
    "isAdmin": false,
    "friends": null,
    "groups": ["users", "staff"],
    "project": {"id": 1, "name": "myproject"}
}

16.1.1. Numbers

{'data1': 1, 'data2': 2.0}

{"data1": 1, "data2": 2.0}

16.1.2. Strings

Fields are always enclosed only by double quote " character

{'data1': 'Alice', "data2": "Apricot"}

{"data1": "Alice", "data2": "Apricot"}

16.1.3. Booleans

Instead of True there is true (lowercase)
Instead of False there is false (lowercase)

{'data1': True, 'data2': False}

{"data1": true, "data2": false}

16.1.4. None

Instead of None there is null

{'data': None}

{"data": null}

16.1.5. Sequences

list is known as array (despite the same syntax)
JSON has no tuple or set
Coma , is not allowed after the last element in list or object
Object of type tuple will serialize as list
Object of type set is not JSON serializable

{'data1': [1, 2, 3], 'data2': (1, 2, 3)}

{"data1": [1, 2, 3], "data2": [1, 2, 3]}

16.1.6. Mappings

dict is known as object (despite the same syntax)
Coma , is not allowed after the last element in list or object

{'data': {'a':1, 'b':2, 'c':3}}

{"data": {"a": 1, "b": 2, "c": 3}}

16.1.7. Identifiers

camelCase is convention, although snake_case is also valid
Fields are always enclosed only by double quote " character

{'is_admin': True}

{"isAdmin": true}

16.1.8. Unicode

Unicode characters are stored as unicode entities ("cze\\u015b\\u0107")

{'data': 'cześć'}

{"data": "cze\\u015b\\u0107"}

16.1.9. JSON or Python?

Python:

{"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", "birthdate": "1995-07-15"},
          {"name": "Rick Martinez", "birthdate": "1996-01-21"},
          {"name": "Alex Vogel", "birthdate": "1994-11-15"},
          {"name": "Chris Beck", "birthdate": "1999-08-02"},
          {"name": "Beth Johanssen", "birthdate": "2006-05-09"},
          {"name": "Mark Watney", "birthdate": "1994-10-12"}]}

JSON:

{"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", "birthdate": "1995-07-15"},
          {"name": "Rick Martinez", "birthdate": "1996-01-21"},
          {"name": "Alex Vogel", "birthdate": "1994-11-15"},
          {"name": "Chris Beck", "birthdate": "1999-08-02"},
          {"name": "Beth Johanssen", "birthdate": "2006-05-09"},
          {"name": "Mark Watney", "birthdate": "1994-10-12"}]}

Both are identical.

16.1.10. Pretty Printing JSON

JSON can be minified to save space for network transmission
Minified JSON is not human readable
Use python -m json.tool to prettify (humanize) output

Minified JSON file:

$ curl https://python3.info/_static/users.json
[{"_clsname": "User", "firstname": "Mark", "lastname": "Watney",
"groups": [{"_clsname": "Group", "gid": 1, "name": "users"}]},
{"_clsname": "User", "firstname": "Melissa", "lastname": "Lewis",
"groups": [{"_clsname": "Group", "gid": 1, "name": "users"},
{"_clsname": "Group", "gid": 2, "name": "admins"}]}, {"_clsname":
"User", "firstname": "Rick", "lastname": "Martinez", "groups": []}]

Pretty Printing JSON:

$ curl https://python3.info/_static/users.json |python -m json.tool
[
  {
    "_type": "User",
    "firstname": "Mark",
    "lastname": "Watney",
    "groups": [
      {
        "_type": "Group",
        "gid": 1,
        "name": "users"
      }
    ]
  },
  {
    "_type": "User",
    "firstname": "Melissa",
    "lastname": "Lewis",
    "groups": [
      {
        "_type": "Group",
        "gid": 1,
        "name": "users"
      },
      {
        "_type": "Group",
        "gid": 2,
        "name": "admins"
      }
    ]
  },
  {
    "_type": "User",
    "firstname": "Rick",
    "lastname": "Martinez",
    "groups": []
  }
]

json.tool checks JSON syntax validity:

$ echo '{"firstname": "Mark", "lastname": "Watney",}' | python -m json.tool
Illegal trailing comma before end of object: line 1 column 43 (char 42)

16.1.11. Use Case - 1

[
    {"firstname": "Mark", "lastname": "Watney", "groups": [
        {"gid": 1, "name": "staff"}]},

    {"firstname": "Melissa", "lastname": "Lewis", "groups": [
        {"gid": 1, "name": "staff"},
        {"gid": 2, "name": "admins"}]},

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

16.1.12. Use Case - 2

[
    {"firstname": "Alice", "lastname": "Apricot", "addresses": [
        {"street": "2101 E NASA Pkwy", "city": "Houston", "postcode": "77058", "region": "Texas", "country": "USA"}
    ]},

    {"firstname": "Bob", "lastname": "Blackthorn", "addresses": [
        {"street": "", "city": "Kennedy Space Center", "postcode": "32899", "region": "Florida", "country": "USA"}
    ]},

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

    {"firstname": "Dave", "lastname": "Durian", "addresses": [
        {"street": "Linder Hoehe", "city": "Cologne", "postcode": "51147", "region": "North Rhine-Westphalia", "country": "Germany"}
    ]},

    {"firstname": "Eve", "lastname": "Elderberry", "addresses": [
        {"street": "", "city": "Космодро́м Байкону́р", "postcode": "", "region": "Кызылординская область", "country": "Қазақстан"},
        {"street": "", "city": "Звёздный городо́к", "postcode": "141160", "region": "Московская область", "country": "Россия"}
    ]},

    {"firstname": "Mallory", "lastname": "Melon", "addresses": []}
]