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Make your dataclasses automatically validate their types

Project description

typed_json_dataclass

Codacy Badge CircleCI codecov PyPI status PyPI version PyPI pyversions MIT license

typed_json_dataclass is a library that augments the Python3.7 dataclass feature in two major ways:

  1. Add a way to recursively grab class dictionary definitions, thus making your dataclass JSON serializable
  2. Add a light amount of type validation to your dataclasses, so that you can validate that the JSON you're being given matches the data types that you're expecting.

By expressing your data as dataclasses, and by having your incoming data validated as it is received, you can easily implement the Data Transfer Object (DTO) pattern in your Python code.

This library can be thought of as a combination of attrs, cattrs, and marshamllow

Getting Started

Install the library from PyPI:

pip install typed_json_dataclass

Use the dataclass decorator just like normal, but add the TypedJsonMixin from this library, to your class definition. This will add 4 new methods to all of your dataclasses:

  1. from_dict()
@classmethod
def from_dict(cls, raw_dict):
    """Given a python dict, create an instance of the implementing class.

    :raw_dict: A dictionary that represents the DTO to create
    :returns: Returns an instance of the DTO, instantiated via the dict
    """
  1. from_json()
@classmethod
def from_json(cls, raw_json):
    """Given a raw json string, create an instance of the implementing class.

    :raw_json: A json string that represents the DTO to create
    :returns: Returns an instance of the DTO, instantiated via the json
    """
  1. to_dict()
def to_dict(self, *, keep_none=False):
    """Express the DTO as a dictionary.

    :returns: Returns the instantiated DTO as a dictionary
    """
  1. to_json()
def to_json(self, *, keep_none=False):
    """Express the DTO as a json string.

    :returns: Returns the instantiated DTO as a json string
    """

Examples

Converting your dataclass to a JSON serializable format

from typing import List
from dataclasses import dataclass
from typed_json_dataclass import TypedJsonMixin

@dataclass
class Person(TypedJsonMixin):
    name: str
    age: int

@dataclass
class Family(TypedJsonMixin):
    people: List[Person]

bob = Person(name='Bob', age=24)
alice = Person(name='Alice', age=32)
family = Family(people=[bob, alice])

print(family.to_json())
# => {"people": [{"name": "Bob", "age": 24}, {"name": "Alice", "age": 32}]}

If your data doesn't match the type definitions, you'll get a helpful error:

from dataclasses import dataclass
from typed_json_dataclass import TypedJsonMixin

@dataclass
class Person(TypedJsonMixin):
    name: str
    age: int

request_data = '{"name":"Bob","age":"24"}'

bob = Person.from_json(request_data)
# => TypeError: Person.age is expected to be <class 'int'>, but value 24 with type <class 'str'> was found instead

And you can parse data from a Python dict as well. Just use the .from_dict() function instead:

from dataclasses import dataclass
from typed_json_dataclass import TypedJsonMixin

@dataclass
class Person(TypedJsonMixin):
    name: str
    age: int

request_data_as_dict = {
    'name': 'Alice',
    'age': '32'
}

alice = Person.from_dict(request_data_as_dict)
# => TypeError: Person.age is expected to be <class 'int'>, but value 32 with type <class 'str'> was found instead

Setting a mapping_mode for auto mapping

from dataclasses import dataclass
from typed_json_dataclass import TypedJsonMixin, MappingMode

@dataclass
class Person(TypedJsonMixin):
    person_name: str
    person_age: int

request_data_as_dict = {
    'personName': 'Alice',
    'personAge': 32
}

alice = Person.from_dict(request_data_as_dict, mapping_mode=MappingMode.SnakeCase)
# => Person(person_name='Alice', person_age=32)

This mapping mode is useful for when you get requests that have the JSON in a camel case format, but you want your objects to be snake case and stay PEP8 compliant.

Changelog

0.2.2 - Sun, 2019-06-02

0.2.1 - Wed, 2019-05-29

  • Upgrade urllib3 to address CVE-2019-11324

0.2.0 - Sat, 2018-1-26

  • Add automatic mapping modes

0.1.1 - Sun, 2018-12-30

  • Correct some lazy tests

0.1.0 - Sun, 2018-12-30

  • We now support recursive ForwardRef type definitions

0.0.2 - Sun, 2018-12-30

  • Added several open source project badges.
  • Added much more useful information to the README.
  • No code/functionality changes.

0.0.1 - Sun, 2018-12-30

  • Created the base project and uploaded it to PyPI. Not much additional work has been done.

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