bagof-magic

Classes that build themselves from your type hints.

Write your fields as annotations. Magic generates __init__, __repr__, __eq__, and everything else.

from bagof.magic import Magic

class Point(Magic, frozen=True):
    x: float
    y: float

>>> Point(1.0, 2.0)
Point(x=1.0, y=2.0)
>>> Point(1.0, 2.0) == Point(1.0, 2.0)
True
>>> Point(1.0, 2.0).x = 3.0
Traceback (most recent call last):
AttributeError: Cannot set frozen field 'x'

If you prefer a decorator:

=== "Base class"

```python
from bagof.magic import Magic

class Point(Magic, frozen=True):
    x: float
    y: float
```

=== "Decorator"

```python
from bagof.magic import magic

@magic(frozen=True)
class Point:
    x: float
    y: float
```

What sets it apart

• Settings are class keyword arguments, and subclasses inherit them. Set frozen=True on a base once; every subclass keeps it, and can override just the settings it needs to change. See Settings.
• Per-field behaviour lives in the annotation, not in a field() call: tags: Factory[list], token: NoRepr[str] = "". See Field annotations.
• Conversion and validation come from the type hint, opt in per class or per field. Config("localhost", "9000") becomes port=9000 because the hint says int. See Conversion and validation.
• A class can build one of its own subclasses, chosen from the arguments it's called with. See Building the right subclass.
• A field can accept several input names, and expose forwarding properties under other names. See Input aliases and forwarding properties.
• A required field can follow one with a default, so a subclass can add one to a base whose fields all have defaults. See Field annotations.
• Also included: dict-like instances, replace/asdict/astuple, mutable defaults that aren't shared, hooks around construction, generic classes, and docstrings generated from the fields. See Extras.

How it compares

Close to attrs in spirit, with pydantic's habit of doing real work from your type hints, and inheritance where the others use decorators.

There is a fuller side-by-side in the comparison page.

Settings

class Thing(Magic, frozen=True, kw_only=True, slots=True):
    ...

Most of them also accept a string instead of True, which binds the generated method under that name. This is useful when you want to call the generated method from your own.

See Settings for how they're inherited and how to override them.

Install

pip install git+https://github.com/bagofseeds/bagof-magic.git

Python 3.8 and later.

Status

Early. The API is settling, and things may still move. Issues and ideas are welcome at bagofseeds/bagof-magic.