Sneak peek

The most simple example of middle and some of its features (using Python 3.6+ syntax):

>>> import typing
>>> import middle

>>> class Address(middle.Model):
...     street_name: str
...     number: typing.Optional[int]
...     city: str

>>> class Person(middle.Model):
...     name: str
...     age: int
...     address: typing.Dict[str, Address]

>>> data = {
...     "name": "John Doe",
...     "age": 42,
...     "address": {
...         "home": {
...             "street_name": "Foo St",
...             "number": None,
...             "city": "Python Park"
...         },
...         "work": {
...             "street_name": "Bar Blvd",
...             "number": "1337",
...             "city": "Park City"
...         }
...     }
... }

>>> person = Person(data)

>>> person
Person(name='John Doe', age=42, address={'home': Address(street_name='Foo St', number=None, city='Python Park'), 'work': Address(street_name='Bar Blvd', number=1337, city='Park City')})

>>> middle.asdict(person)
{'name': 'John Doe', 'age': 42, 'address': {'home': {'street_name': 'Foo St', 'number': None, 'city': 'Python Park'}, 'work': {'street_name': 'Bar Blvd', 'number': 1337, 'city': 'Park City'}}}

Wanted a more complex example, with Python 3.5 compatible syntax? For sure!

>>> from typing import Dict, List
>>> import middle

>>> class Game(middle.Model):
...     name: str = middle.field()
...     score: float = middle.field(minimum=0, maximum=10)
...     resolution_tested: str = middle.field(pattern="^\d+x\d+$")
...     genre: List[str] = middle.field(unique_items=True)
...     rating: Dict[str, float] = middle.field(max_properties=5)

>>> data = {
...     "name": "Cities: Skylines",
...     "score": 9.0,
...     "resolution_tested": "1920x1200",
...     "genre": ["Simulators", "City Building"],
...     "rating": {
...         "IGN": 8.5,
...         "Gamespot": 8.0,
...         "Steam": 4.5
...     }
... }

>>> game = Game(**data)

>>> game
Game(name='Cities: Skylines', score=9.0, resolution_tested='1920x1200', genre=['Simulators', 'City Building'], rating={'IGN': 8.5, 'Gamespot': 8.0, 'Steam': 4.5})

>>> middle.asdict(game)
{'name': 'Cities: Skylines', 'score': 9.0, 'resolution_tested': '1920x1200', 'genre': ['Simulators', 'City Building'], 'rating': {'IGN': 8.5, 'Gamespot': 8.0, 'Steam': 4.5}}

middle is flexible enough to understand Enum, nested models and a large variety of types declared on the typing module out of the box. Also, you can extend it to your own classes!

Done

• If possible, fine grain the converters, so a str input value of {} doesn’t end up as str({});

• Get date and datetime converters to be customizable, instead of an if isinstance statement;

• Implement more validators and a registerable for more metadata options;

• Implement a better “type dispatcher” based on more complex rules (other than type(field.type) delivered by functools.singledispatch) because the typing module has changed a bit between Python 3.6 and 3.7;

• Support more types (typing.Tuple, decimal.Decimal);

• Get 100% (or closer) in code coverage;

• Lots of documentation;

• Python 3.5 support (with the exception of Windows platforms, see warning for Windows developers below);

Future discussions

• In Python 3.7, a neat feature was added: dataclasses. I know it sounds really awesome to not depend on a 3rd-party library - such as attrs, but the latest provides a lot of functionalities that can’t be found on Python 3.7 dataclasses (for now), so I’ll leave this open for further discussion.

Warning for Windows developers

If you’re using Windows and Python 3.5, I think middle would not work well for you. CI in AppVeyor was disabled for Python 3.5 because of this issue. If Guido doesn’t care, why should I (or you) ?

Useful links

• Source code

• Issues

v0.2.2 on 2018-10-28

• Added the possibility for models to have methods, functions, properties and etc.

v0.2.1 on 2018-07-26

• Quick fix related to the change log and MANIFEST.in files

v0.2.0 on 2018-07-26

• Released (part) of the documentation

• Got 99% coverage (finally combined)

• Python 3.5 support added

v0.1.1 on 2018-07-02

• Add proper unit testing and support for Python 3.6 and 3.7

• Made the API a bit more flexible

• Code format and check done with black

v0.1.0 on 2018-06-21

• First release on PyPI.