6.3. JSON To File

6.3.1. Rationale

  • file extension .json

  • json.load(file) -> dict

  • json.dump(data, file) -> None

6.3.2. Write

def dump(obj: Any,
         fp: IO[str],
         *,
         skipkeys: bool = ...,
         ensure_ascii: bool = ...,
         check_circular: bool = ...,
         allow_nan: bool = ...,
         cls: Type[JSONEncoder] | None = ...,
         indent: None | int | str = ...,
         separators: tuple[str, str] | None = ...,
         default: (Any) -> Any | None = ...,
         sort_keys: bool = ...,
         **kwds: Any) -> None

Serialize to JSON:

>>> import json
>>>
>>>
>>> FILE = r'_temporary.json'
>>>
>>> DATA = {'firstname': 'Mark',
...         'lastname': 'Watney'}
>>>
>>>
>>> with open(FILE, mode='w') as file:
...     json.dump(DATA, file)
>>>
>>> result = open(FILE).read()
>>> print(result)
{"firstname": "Mark", "lastname": "Watney"}

6.3.3. Read

def load(fp: SupportsRead[str | bytes],
         *,
         cls: Type[JSONDecoder] | None = ...,
         object_hook: (dict) -> Any | None = ...,
         parse_float: (str) -> Any | None = ...,
         parse_int: (str) -> Any | None = ...,
         parse_constant: (str) -> Any | None = ...,
         object_pairs_hook: (list[tuple[Any, Any]]) -> Any | None = ...,
         **kwds: Any) -> Any

Serialize to JSON:

>>> import json
>>>
>>>
>>> FILE = r'_temporary.json'
>>> DATA = '{"firstname": "Mark", "lastname": "Watney"}'
>>> _ = open(FILE, mode='w').write(DATA)
>>>
>>>
>>> with open(FILE) as file:
...     result = json.load(file)
>>>
>>> print(result)
{'firstname': 'Mark', 'lastname': 'Watney'}

6.3.4. Assignments

Code 6.1. Solution
"""
* Assignment: JSON Read/Write Dump
* Complexity: easy
* Lines of code: 4 lines
* Time: 8 min

English:
    1. Extract from input a header and data
    2. Create `result: list[dict]`
        a. key - name from the header
        b. value - measurement or species
    3. Write structure to file `FILE` in JSON format
    4. Run doctests - all must succeed

Polish:
    1. Z danych wydziel nagłówek i pomiary
    2. Wygeneruj `result: list[dict]`
        a. klucz - nazwa z nagłówka
        b. wartość - wyniki pomiarów lub gatunek
    3. Zapisz strukturę do pliku `FILE` w formacie JSON
    4. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0

    >>> type(result)
    <class 'list'>
    >>> len(result) > 0
    True
    >>> all(type(row) is dict
    ...     for row in result)
    True
    >>> from os import remove
    >>> result = open(FILE).read()
    >>> remove(FILE)
    >>> print(result)  # doctest: +NORMALIZE_WHITESPACE
    [{"Sepal length": 5.8, "Sepal width": 2.7, "Petal length": 5.1, "Petal width": 1.9, "Species": "virginica"},
     {"Sepal length": 5.1, "Sepal width": 3.5, "Petal length": 1.4, "Petal width": 0.2, "Species": "setosa"},
     {"Sepal length": 5.7, "Sepal width": 2.8, "Petal length": 4.1, "Petal width": 1.3, "Species": "versicolor"},
     {"Sepal length": 6.3, "Sepal width": 2.9, "Petal length": 5.6, "Petal width": 1.8, "Species": "virginica"},
     {"Sepal length": 6.4, "Sepal width": 3.2, "Petal length": 4.5, "Petal width": 1.5, "Species": "versicolor"},
     {"Sepal length": 4.7, "Sepal width": 3.2, "Petal length": 1.3, "Petal width": 0.2, "Species": "setosa"},
     {"Sepal length": 7.0, "Sepal width": 3.2, "Petal length": 4.7, "Petal width": 1.4, "Species": "versicolor"},
     {"Sepal length": 7.6, "Sepal width": 3.0, "Petal length": 6.6, "Petal width": 2.1, "Species": "virginica"},
     {"Sepal length": 4.9, "Sepal width": 3.0, "Petal length": 1.4, "Petal width": 0.2, "Species": "setosa"}]
"""

FILE = '_temporary.json'

DATA = [
    ('Sepal length', 'Sepal width', 'Petal length', 'Petal width', 'Species'),
    (5.8, 2.7, 5.1, 1.9, 'virginica'),
    (5.1, 3.5, 1.4, 0.2, 'setosa'),
    (5.7, 2.8, 4.1, 1.3, 'versicolor'),
    (6.3, 2.9, 5.6, 1.8, 'virginica'),
    (6.4, 3.2, 4.5, 1.5, 'versicolor'),
    (4.7, 3.2, 1.3, 0.2, 'setosa'),
    (7.0, 3.2, 4.7, 1.4, 'versicolor'),
    (7.6, 3.0, 6.6, 2.1, 'virginica'),
    (4.9, 3.0, 1.4, 0.2, 'setosa')]

Code 6.2. Solution
"""
* Assignment: JSON Read/Write Load
* Complexity: easy
* Lines of code: 4 lines
* Time: 8 min

English:
    1. Read data from `FILE`
    2. Convert data to `result: list[tuple]`
    3. Do not add header as a first line
    4. Run doctests - all must succeed

Polish:
    1. Odczytaj dane z pliku `FILE`
    2. Przekonwertuj dane do `result: list[tuple]`
    3. Nie dodawaj nagłówka jako pierwsza linia
    4. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0

    >>> type(result)
    <class 'list'>
    >>> len(result) > 0
    True
    >>> all(type(row) is tuple
    ...     for row in result)
    True
    >>> result  # doctest: +NORMALIZE_WHITESPACE
    [(5.8, 2.7, 5.1, 1.9, 'virginica'),
     (5.1, 3.5, 1.4, 0.2, 'setosa'),
     (5.7, 2.8, 4.1, 1.3, 'versicolor'),
     (6.3, 2.9, 5.6, 1.8, 'virginica'),
     (6.4, 3.2, 4.5, 1.5, 'versicolor'),
     (4.7, 3.2, 1.3, 0.2, 'setosa'),
     (7.0, 3.2, 4.7, 1.4, 'versicolor'),
     (7.6, 3.0, 6.6, 2.1, 'virginica'),
     (4.9, 3.0, 1.4, 0.2, 'setosa')]
     >>> from os import remove
     >>> remove(FILE)
"""

FILE = r'_temporary.json'

DATA = """[{"Sepal length": 5.8, "Sepal width": 2.7, "Petal length": 5.1, "Petal width": 1.9, "Species": "virginica"},
{"Sepal length": 5.1, "Sepal width": 3.5, "Petal length": 1.4, "Petal width": 0.2, "Species": "setosa"},
{"Sepal length": 5.7, "Sepal width": 2.8, "Petal length": 4.1, "Petal width": 1.3, "Species": "versicolor"},
{"Sepal length": 6.3, "Sepal width": 2.9, "Petal length": 5.6, "Petal width": 1.8, "Species": "virginica"},
{"Sepal length": 6.4, "Sepal width": 3.2, "Petal length": 4.5, "Petal width": 1.5, "Species": "versicolor"},
{"Sepal length": 4.7, "Sepal width": 3.2, "Petal length": 1.3, "Petal width": 0.2, "Species": "setosa"},
{"Sepal length": 7.0, "Sepal width": 3.2, "Petal length": 4.7, "Petal width": 1.4, "Species": "versicolor"},
{"Sepal length": 7.6, "Sepal width": 3.0, "Petal length": 6.6, "Petal width": 2.1, "Species": "virginica"},
{"Sepal length": 4.9, "Sepal width": 3.0, "Petal length": 1.4, "Petal width": 0.2, "Species": "setosa"}]"""

with open(FILE, mode='w') as file:
    file.write(DATA)

result: list = []