Desert: DRY deserialization

docs
code
tests
package

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.

Installation

pip install desert

or with Poetry

poetry add desert

Usage

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

@dataclass
class Person:
    name: str
    age: int

@dataclass
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)])

Documentation

https://desert.readthedocs.io/

Limitations

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

Acknowledgements

• This package began as an extension of marshmallow-dataclass to add support for attrs.

Contents

Desert: DRY deserialization

docs
code
tests
package

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.

Installation

pip install desert

or with Poetry

poetry add desert

Usage

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

@dataclass
class Person:
    name: str
    age: int

@dataclass
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)])

Documentation

https://desert.readthedocs.io/

Limitations

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

Acknowledgements

• This package began as an extension of marshmallow-dataclass to add support for attrs.

Installation

At the command line:

pip install desert

or with Poetry

poetry add desert

Usage

Basics

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

@dataclass
class Person:
    name: str
    age: int

@dataclass
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)])

Desert can be used with dataclasses or attr. With either module, Desert is able to infer the appropriate marshmallow field for any of these types:

• int

• float

• bool

• str

• datetime.datetime

• datetime.time

• datetime.timedelta

• datetime.date

• uuid.UUID

• decimal.Decimal

• enum.Enum (if you have marshmallow_enum installed.)

• typing.Union (if you have marshmallow_union installed, tries each type until one succeeds.)

There are two syntaxes for specifying a field.

In the more concise form, desert.field() wraps dataclasses.field() and desert.ib() wraps attr.ib(). These functions take a marshmallow.fields.Field as the first argument, and the remaining arguments are forwarded to the corresponding wrapped function.

In the more verbose form, simply use the normal functions dataclasses.field() and attr.ib(), but provide the metadata value using desert.metadata(), which returns a dict of values namespaced for desert to use.

Use with dataclasses

import dataclasses
import datetime

import desert
import marshmallow


@dataclasses.dataclass
class Entry:

    timestamp: str = desert.field(marshmallow.fields.NaiveDateTime())

    # Or use the more verbose form.
    favorite_number: int = dataclasses.field(default=3, metadata=desert.metadata(field=marshmallow.fields.Int()))

schema = desert.schema(Entry)

print(schema.load({"timestamp": "2019-10-21T10:25:00", "favorite_number": 42}))

Entry(timestamp=datetime.datetime(2019, 10, 21, 10, 25), favorite_number=42)

Use with attrs

import datetime

import attr
import desert
import marshmallow


@attr.dataclass
class Entry:

    timestamp: str = desert.ib(marshmallow.fields.NaiveDateTime())

    # Or use the more verbose form.
    favorite_number: int = attr.ib(default=3, metadata=desert.metadata(field=marshmallow.fields.Int()))

schema = desert.schema(Entry)

print(schema.load({"timestamp": "2019-10-21T10:25:00", "favorite_number": 42}))

Entry(timestamp=datetime.datetime(2019, 10, 21, 10, 25), favorite_number=42)

Schema meta parameters

Any marshmallow.Schema.Meta value is accepted in the meta dict. For example, to exclude unknown values during deserialization:

import attr
import desert

@attr.dataclass
class A:
    x: int

schema = desert.schema_class(A, meta={"unknown": marshmallow.EXCLUDE})()
print(schema.load({"x": 1, "y": 2}))

A(x=1)

Reference

desert package

Submodules

desert.exceptions module

exception desert.exceptions.DesertException

Bases: Exception

Top-level exception for desert.

exception desert.exceptions.NotAnAttrsClassOrDataclass

Bases: desert.exceptions.DesertException

Raised for dataclass operations on non-dataclasses.

exception desert.exceptions.UnknownType

Bases: desert.exceptions.DesertException

Raised for a type with unknown serialization equivalent.

Module contents

desert.field(marshmallow_field, **kw)

Specify a marshmallow field in the metadata for a dataclasses.dataclass.

@dataclasses.dataclass
class A:
    x: int = desert.field(marshmallow.fields.Int())

Return type

Field

desert.ib(marshmallow_field, **kw)

Specify a marshmallow field in the metadata for an attr.dataclass.

@attr.dataclass
class A:
    x: int = desert.ib(marshmallow.fields.Int())

Return type

_CountingAttr

desert.metadata(field)

Specify a marshmallow field in the field metadata.

x: int = attr.ib(metadata=desert.metadata(marshmallow.fields.Int()))

desert.schema(cls, many=False, meta={})

Build a marshmallow schema instance for the class.

Parameters

• cls (Type) – A type-hinted attrs class or dataclass.

• meta (Dict[str, Any]) – The schema’s Meta class will be built from this dict. Use values from marshmallow.Schema.Meta.

Return type

Schema

Returns

An instance of the marshmallow schema for the class.

desert.schema_class(cls, meta={})

Build a marshmallow schema class for the class.

Parameters

• cls (Type) – A type-hinted attrs class or dataclass.

• meta (Dict[str, Any]) – The schema’s Meta class will be built from this dict. Use values from marshmallow.Schema.Meta.

Return type

Type[Schema]

Returns

The marshmallow schema class.

Contributing

Contributions are welcome, and they are greatly appreciated! Every little bit helps, and credit will always be given.

Bug reports

When reporting a bug please include:

• Your operating system name and version.

• Any details about your local setup that might be helpful in troubleshooting.

• Detailed steps to reproduce the bug.

Documentation improvements

desert could always use more documentation, whether as part of the official desert docs, in docstrings, or even on the web in blog posts, articles, and such.

Feature requests and feedback

The best way to send feedback is to file an issue at https://github.com/python-desert/desert/issues.

If you are proposing a feature:

• Explain in detail how it would work.

• Keep the scope as narrow as possible, to make it easier to implement.

• Remember that this is a volunteer-driven project, and that code contributions are welcome :)

Development

To set up desert for local development:

1. Fork desert (look for the “Fork” button).

2. Clone your fork locally:

   git clone git@github.com:your_name_here/desert.git
   

3. Create a branch for local development:

   git checkout -b name-of-your-bugfix-or-feature
   

   Now you can make your changes locally.

4. When you’re done making changes, run all the checks, doc builder and spell checker with tox one command:

   tox
   

5. Commit your changes and push your branch to GitHub:

   git add .
   git commit -m "Your detailed description of your changes."
   git push origin name-of-your-bugfix-or-feature
   

6. Submit a pull request through the GitHub website.

Pull Request Guidelines

If you need some code review or feedback while you’re developing the code just make the pull request.

For merging, you should:

1. Include passing tests (run tox) 1.

2. Update documentation when there’s new API, functionality etc.

3. Add a file in changelog.d/ describing the changes. The filename should be {id}.{type}.rst, where {id} is the number of the GitHub issue or pull request and {type} is one of breaking (for breaking changes), deprecation (for deprecations), or change (for non-breaking changes). For example, to add a new feature requested in GitHub issue #1234, add a file called changelog.d/1234.change.rst describing the change.

4. Add yourself to AUTHORS.rst.

1

If you don’t have all the necessary python versions available locally you can rely on Travis - it will run the tests for each change you add in the pull request.

It will be slower though …

Tips

To run a subset of tests:

tox -e envname -- pytest -k test_myfeature

To run all the test environments in parallel (you need to pip install detox):

detox

Authors

A full list of contributors is available in the GitHub repository.

Changelog

2020.11.18 (2020-11-18)

Changes

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

---

2020.01.06 (2020-01-06)

Changes

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

---

2020.01.05 (2020-01-05)

Changes

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

---

2020.01.04 (2020-01-04)

Changes

• Add support for Tuple[int, …] per https://docs.python.org/3/library/typing.html#typing.Tuple #16 Thanks to @sveinse for reporting and testing.

• Use module imports internally. #18

• Desert version only needs to be updated in _version.py #19

• Fix doctests. #20

---

2020.01.03

Changes

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

2019.12.18

Changes

• Improve error message for unknown generics. #10

2019.12.10

Changes

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

2019.12.09

Changes

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

2019.11.06 (2019-11-06)

Changes

• Add twine and wheel development dependencies. #2

---

2019.11.06 (2019-11-06)

Changes

• 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)

Changes

• First release on PyPI.

—

Indices and tables

• Index

• Module Index

• Search Page