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Define real, inheritable, and efficient Python classes using variable annotations

Project description

typedobject

Define real, inheritable, and efficient Python classes using TypedDict-like syntax.

Getting started

Install from pip.

python -m pip install typedobject

Then, annotate your class with typedobject and declare its member fields using variable annotations.

from typedobject import typedobject

@typedobject
class Point:
    x: int
    y: int

Then construct the object using either positional or keyword arguments.

pt1 = Point(10, 20)
pt2 = Point(x=10, y=20)
assert pt1 == pt2

You can define methods, including __init__.

@typedobject
class Rectangle:
    pt1: Point
    pt2: Point

    def __init__(self, x1, y1, x2, y2):
        self.pt1 = Point(x1, y1)
        self.pt2 = Point(x2, y2)

    def area(self):
        return (self.pt2.x - self.pt1.x) * (self.pt2.y - self.pt1.y)

rect = Rectangle(1, 1, 3, 3)
assert rect.area() == 4

Unlike TypedDict, the defined classes are actually fresh new classes, not dicts.

assert isinstance(rect, Rectangle)
assert not isinstance(rect, Point)

Inheritance works just fine.

@typedobject
class RoundedRect(Rectangle):
    corner_radius: int

rr = RoundedRect(Point(1, 1), Point(3, 3), 1)

Note that the derived class overrides __init__, unless you use .no_init.

@typedobject.no_init
class RoundedRect2(Rectangle):
    corner_radius: int

rr = RoundedRect2(1, 1, 3, 3)
assert not hasattr(rr, 'corner_radius')

Typed object classes, unlike dataclass, specify __slots__, which makes access to attributes faster and makes objects take less memory, but prevents adding new fields dynamically.

They also prevent multiple inheritance.

# raises TypeError
class RectangleWithAPoint(Rectangle, Point):
    pass

You can, however, inject mixins.

class TwoDObjectMixin:
    def area(self):
        return self.width() * self.height()

@typedobject
class Rectangle2(TwoDObjectMixin):
    pt1: Point
    pt2: Point

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