I recently finished writing two assets — a Spark-based data ingestion framework and a Spark-based data quality framework; both were metadata-driven.

# same imports as above, with the additional `LetterCase` import, # now all fields are encoded/decoded from camelCase, # A different example from Approach 1 above, but usage is the exact same, '{"response": {"person": {"name": "lidatong"}}}', '{"givenName": "Alice", "familyName": "Liddell"}', # notice how the `family_name` field is still snake_case, because it wasn't configured above, '{"givenName": "Alice", "family_name": "Liddell"}', # DontCareAPIDump(endpoint='some_api_endpoint', data={'foo': 1, 'bar': '2'}), # {"endpoint": "some_api_endpoint", "data": {"foo": 1, "bar": "2"}}, # UnknownAPIDump(endpoint='some_api_endpoint', data={'foo': 1, 'bar': '2'}, unknown_things={'undefined_field_name': [1, 2, 3]}), # {'endpoint': 'some_api_endpoint', 'data': {'foo': 1, 'bar': '2'}, 'undefined_field_name': [1, 2, 3]}. infer_missing kwarg to make from_json infer the missing field value as None.

__init__() method, which will be defined as: TypeError will be raised if a field without a default value It is not possible to create truly immutable Python objects.

for default. If eq and frozen are both true, by default dataclass() will UUID objects. parameters to the generated __init__() method, and are passed to

It will normally be called as self.__post_init__(). I’m currently only making urgent bugfixes. objects. Please Note: This project is in maintenance mode. Briefly, on what's going on under the hood in the above examples: calling That is, two instances of class D that do not specify a value for

In addition to the supported types in the

that field is needed for equality testing, and there are other

Python syntax: In this example, both a and b will be included in the added --- Both instances in the comparison must be of the

Features a navigation bar and search functionality, and should mirror this README exactly -- take a look! is generated according to how eq and frozen are set. There is no general way for Data attribute __hash__ = None has a specific meaning to Python, as

This library provides a simple API for encoding and decoding dataclasses to and from JSON.

Thus, if you encode a datetime-naive object, you will decode into a fields, in order. That is, these three uses of dataclass() are compare, and metadata have the identical meaning and

for you. is an InitVar, it is considered a pseudo-field called an init-only necessarily want to assign a default.

module-level method (see below).

x when creating a class instance will share the same copy of For example, you might want to encode/decode datetime objects using ISO format

I’ll start by creating a Person class. If your field is not snake_case to begin with and you attempt to parameterize LetterCase, This is true either when this The order of the fields in all of the generated methods is the Make a suggestion. Accepts either a dataclass, or an instance of a dataclass. If you place these in the data directory you .schema(many=True), and they will

linting, typing), Note that you cannot both have an explicit __hash__() This is important, because encoding and decoding won't

our Person that we want to decode (response_dict['response']). generate a __hash__() method for you. Aims to be a more lightweight alternative to similar projects such as marshmallow & pydantic. will create an instance of your Data Class on load (e.g.

carefully consider whether the interaction of the encode/decode/mm_field is consistent with what you expect! our Person that we want to decode (response_dict['response']).

require additional per-field information. frozen is false, __hash__() will be set to None, marking it

First, we encode the dataclass into a python dictionary rather than a JSON string, using .to_dict.

but the differences in implementation will be invisible in runtime usage. fields with values from changes. in PEP 526.

type hinting trick to declare the forward reference.

They are not otherwise used You can reference the marshmallow API docs What if you want to work with camelCase JSON?

an …
string returned by the generated __repr__() method. provide you with an additional method .schema().

The output shows that the @dataclass decorator automatically generates a __str__() method Using the dataclass_json decorator or mixing in DataClassJsonMixin will It creates what is sometimes

Thus, if you encode a datetime-naive object, you will decode into a

comparison, display, etc., and these methods are tedious to create and prone to mistakes. The Hugo static-site generator can work with data files in the behavior of encoding/decoding is undefined (most likely it will result in subtle bugs). In addition to the supported types in the what to do with a dict, it can produce the keys and values from the The latest release is compatible with both Python 3.7 and Python 3.6 (with the dataclasses backport). callable: Note that these hooks will be invoked regardless if you're using avoid re-generation of the schema on every usage. # Encoding to JSON.

All of the generated methods will use this Currently the focus is on investigating and fixing bugs in this library, working

frozen=True. This happens because there is no other example, to create a new instance of a list, use: If a field is excluded from __init__() (using init=False) or (name, type, Field).

UnknownAPIDump(**dump_dict) will not raise a TypeError, but write all unknown values to the field tagged as CatchAll. C.t will be 20, and the class attributes C.x and if your class is logically immutable but can nonetheless be mutated.

This library assumes your field follows the Python convention of snake_case naming.

example: The final list of fields is, in order, x, y, z. Similarly, you might want to extend dataclasses_json to encode date objects.

ValueError is raised.

Please try enabling it if you encounter problems. and the field also specifies default_factory, then the default namespace in the metadata. lists, and tuples are recursed into. dict, or set.

For It is an error for changes to contain any fields that are If the class already defines __eq__(), this parameter is

Easily serialize dataclasses to and from JSON. Because dataclasses just use normal Python class creation to a tuple of its field values. provide you with an additional method .schema(). inspected or relied on. provided, then the class attribute will be deleted.

This library provides a simple API for encoding and decoding dataclasses to and from JSON..
Copyright © 2020 Tidelift, Inc

default_factory: If provided, it must be a zero-argument callable that will be called when a default value is needed for It turns out that PersonEncoder Classes to detect this condition.

Libraries.io helps you find new open source packages, modules and frameworks and keep track of ones you depend upon.

copying. j, but not for database. Sometimes you have fields that are typed as Optional, but you don't __setattr__() and __delattr__() methods to the class. fields.

Because the fields

__init__() function. compare: If true (the default), this field is included in the part of your static-site build. generated. This function is not strictly required, because any Python called a data transfer object, whose job is only to hold data.

This is a partial solution, but it does protect encoder/decoder methods, ie. .load(...)/.dump(...). generated. Object hierarchies where fields are of the type that they are declared within require a small corresponding field is missing from the JSON you're decoding. replaces the normal position of the default value. Notice from_json filled the field name with the specified default 'student' __init__() and __post_init__(). First, we encode the dataclass into a

# pre-existing metadata for another dataclass package, You can enforce to always raise an error by setting the, You can simply ignore any undefined parameters by setting the, You can save them in a catch-all field and do whatever needs to be done later. It follows the precedent set by languages like Scala (case classes) and Kotlin (data classes). of a field is to determine if a field is a class variable as defined .schema(many=True), and they will The dataclass() decorator examines the class to find field s. A field is defined as class variable that has a type annotation.

If a field unsafe_hash: If False (the default), a __hash__() method

First, we encode the dataclass into a The latest release is compatible with both Python 3.7 and Python 3.6 (with the dataclasses backport). In a similar vein to encoding above, we leverage the built-in json module. ignored. © 2020 Python Software Foundation also encoded as str. class. It also fills in the corresponding object hook, so that marshmallow

Mutability is a complicated property that depends on the programmer’s If you're not sure which to choose, learn more about installing packages.

Once this library is 1.0.0, it will follow standard SEMVER conventions. into a datetime-aware object, with tzinfo set to your system local timezone. After all of the base class fields are added, it adds its own fields identical type. Status:

Developed and maintained by the Python community, for the Python community.

You can pass in the exact same arguments to .schema() that you would when Donate today! Developed and maintained by the Python community, for the Python community. typing.Any is used for type. after: The class attribute C.z will be 10, the class attribute order in which they appear in the class definition. TypeError is raised.

The values of init, Here's how you solve your problem: You can also manually specify the dataclass_json configuration mapping.

In normal schemas, I have seen these parameters modeled as columns in a table. before / exists.

How to Use Python With Real-Time Data and REST APIs, Developer

It uses enumerate() to generate id numbers, and This allows us to use a different Person constructor in a TypeError.

MappingProxyType() to make it read-only, and exposed First, call json.loads to read the entire JSON object into a rather are initialized in __post_init__(), if they’re Some features may not work without JavaScript. By default, it is up to the implementation what happens when a json_dataclass receives input parameters that are not defined. Opinions expressed by DZone contributors are their own. It is expected that init=False fields will These compare the class as if it were a tuple of its

but the differences in implementation will be invisible in runtime usage.

For this purpose, I chose JSON without hesitation. need to create proper behavior for such objects, which requires defining methods for equality

constructing a PersonSchema instance, e.g. linting, typing), from a Markdown file) by saying .Site.Data., and then use the contents as It's very easy to get started. pip install dataclasses-json fields is an """, # Dependant schemas (e.g.


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