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Deserialize to objects while staying DRY

Project description

Desert generates serialization schemas for dataclasses and attrs classes. Writing code that’s DRY (“don’t repeat yourself”) helps avoid bugs and improve readability. Desert helps you write code that’s DRY.


pip install desert

or with Poetry

poetry add desert


A simple example models two Person objects in a Car.

from dataclasses import dataclass

# Or using attrs
# from attr import dataclass

from typing import List

import desert

class Person:
    name: str
    age: int

class Car:
    passengers: List[Person]

# Load some simple data types.
data = {'passengers': [{'name': 'Alice', 'age': 21}, {'name': 'Bob', 'age': 22}]}

# Create a schema for the Car class.
schema = desert.schema(Car)

# Load the data.
car = schema.load(data)
assert car == Car(passengers=[Person(name='Alice', age=21), Person(name='Bob', age=22)])



String annotations and forward references inside of functions are not supported.


2022.09.22 (2022-09-22)

Backward-incompatible Changes

  • Update all project dependencies and fix all deprecated warnings. Python 3.6 support was dropped to allow updating deprecated dependencies. #161


  • It is now possible to use type-variant generics in your dataclasses, such as Sequence or MutableSequence instead of List, Mapping instead of Dict, etc.

    This allows you to hide implementation details from users of your dataclasses. If a field in your dataclass works just as fine with a tuple as a list, you no longer need to force your users to pass in a list just to satisfy type checkers.

    For example, by using Mapping or MutableMapping, users can pass OrderedDict to a Dict attribute without MyPy complaining.

    class OldWay:
        str_list: List[str]
        num_map: Dict[str, float]
    # MyPy will reject this even though Marshmallow works just fine. If you use
    # type-variant generics, MyPy will accept this code.
    instance = OldClass([], collections.ChainMap(MY_DEFAULTS))
    class NewWay:
        str_list: List[str]  # Type-invariants still work
        num_map: MutableMapping[str, float]  # Now generics do too


2020.11.18 (2020-11-18)


  • Schemas no longer copy non-field dataclass attributes. Thanks to @sveinse for report and test. #79

2020.01.06 (2020-01-06)


  • Additional metadata are supported in ib() and fields(). Thanks to @sveinse for reporting and testing. #28

2020.01.05 (2020-01-05)


  • Add support for attrs factories that take self (attr.Factory(..., takes_self=True)). #27

2020.01.04 (2020-01-04)




  • Optional fields allow None. #11. Thanks to @sveinse for reporting and testing.



  • Improve error message for unknown generics. #10



  • Add UnknownType exception with better error message for types that should be generic. #8



  • Marshmallow schema Meta arguments are accepted, allowing exclusion of unknown fields and other options. #3

2019.11.06 (2019-11-06)


  • Add twine and wheel development dependencies. #2

2019.11.06 (2019-11-06)


  • Switch to calver

Backward-incompatible Changes

  • Non-optional fields without a default or factory now have required=True so raise marshmallow.exceptions.ValidationError when missing. #1

0.1.0 (2019-06-22)


  • First release on PyPI.

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