JSON

In order to better support JSON, you should declare each of your class that supports being converted to JSON with

class satella.json.JSONAble
abstract to_json()

Return a JSON-able representation of this object

Return type:

Jsonable

class satella.json.JSONAbleDataObject(**kwargs)

A data-class that supports conversion of its classes to JSON

Define like this:

>>> class CultureContext(JSONAbleDataObject):
>>>     language: str
>>>     timezone: str
>>>     units: str = 'metric'

Note that type annotation is mandatory and default values are supported. Being data value objects, these are eq-able and hashable.

And use like this:

>>> a = CultureContext(language='pl', timezone='Europe/Warsaw')
>>> assert a.to_json() == {'language': 'pl', 'timezone': 'Europe/Warsaw', 'units': 'metric'}
>>> assert CultureContext.from_json(a.to_json) == a
Raises:

ValueError – a non-default value was not provided

to_json()

Convert self to JSONable value

Return type:

Dict

Then you can convert structures made out of standard serializable Python JSON objects, such as dicts and lists, and also JSONAble objects, by this all

satella.json.json_encode(x)

Convert an object to JSON. Will properly handle subclasses of JSONAble

Parameters:

x (Any) – object to convert

Return type:

str

You might also want to check out the JSONEncoder satella uses to do it.

class satella.json.JSONEncoder(*, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, sort_keys=False, indent=None, separators=None, default=None)

This encoder will encode everything!

enums will be dumped to their value.

Constructor for JSONEncoder, with sensible defaults.

If skipkeys is false, then it is a TypeError to attempt encoding of keys that are not str, int, float or None. If skipkeys is True, such items are simply skipped.

If ensure_ascii is true, the output is guaranteed to be str objects with all incoming non-ASCII characters escaped. If ensure_ascii is false, the output can contain non-ASCII characters.

If check_circular is true, then lists, dicts, and custom encoded objects will be checked for circular references during encoding to prevent an infinite recursion (which would cause an RecursionError). Otherwise, no such check takes place.

If allow_nan is true, then NaN, Infinity, and -Infinity will be encoded as such. This behavior is not JSON specification compliant, but is consistent with most JavaScript based encoders and decoders. Otherwise, it will be a ValueError to encode such floats.

If sort_keys is true, then the output of dictionaries will be sorted by key; this is useful for regression tests to ensure that JSON serializations can be compared on a day-to-day basis.

If indent is a non-negative integer, then JSON array elements and object members will be pretty-printed with that indent level. An indent level of 0 will only insert newlines. None is the most compact representation.

If specified, separators should be an (item_separator, key_separator) tuple. The default is (’, ‘, ‘: ‘) if indent is None and (‘,’, ‘: ‘) otherwise. To get the most compact JSON representation, you should specify (‘,’, ‘:’) to eliminate whitespace.

If specified, default is a function that gets called for objects that can’t otherwise be serialized. It should return a JSON encodable version of the object or raise a TypeError.

default(o)

Implement this method in a subclass such that it returns a serializable object for o, or calls the base implementation (to raise a TypeError).

For example, to support arbitrary iterators, you could implement default like this:

def default(self, o):
    try:
        iterable = iter(o)
    except TypeError:
        pass
    else:
        return list(iterable)
    # Let the base class default method raise the TypeError
    return JSONEncoder.default(self, o)
Parameters:

o (Any) –

Return type:

Jsonable

This will serialize unknown objects in the following way. First, __dict__ will be extracted out of this object. The dictionary will be constructed in such a way, that for each key in this __dict__, it’s value’s repr will be assigned.

satella.json.read_json_from_file(path)

Load a JSON from a provided file, as UTF-8 encoded plain text.

Parameters:

path (str) – path to the file

Returns:

JSON content

Raises:
  • ValueError – the file contained an invalid JSON

  • OSError – the file was not readable or did not exist

Return type:

JSONAble

satella.json.write_json_to_file(path, value, **kwargs)

Write out a JSON to a file as UTF-8 encoded plain text.

This will use Satella’s JSONEncoder internally.

Parameters:
  • path (str) – path to the file

  • value (JSONAble) – JSON-able content

  • kwargs – Legacy argument do not use it, will raise a warning upon non-empty. This never did anything.

Return type:

None

satella.json.write_json_to_file_if_different(path, value, encoding='utf-8', **kwargs)

Read JSON from a file. Write out a JSON to a file if it’s value is different, as UTF-8 encoded plain text.

This will use Satella’s JSONEncoder internally.

Parameters:
  • path (str) – path to the file

  • value (JSONAble) – JSON-able content

  • encoding (str) – encoding to use while parsing the contents of the file

  • kwargs – will be passed to ujson/json dumps

Returns:

whether the write actually happened

Return type:

bool