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07-metaclasses.py
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07-metaclasses.py
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from math import pi
class TypeChecker:
required_type = object
def __init__(self, name=None):
self.name = f'_{name}'
def __get__(self, instance, owner=None):
return instance.__dict__[self.name]
def __set__(self, instance, value):
assert isinstance(value, self.required_type), \
f'Booooo! Expecting a {self.required_type.__name__}'
instance.__dict__[self.name] = value
def type_check(cls):
for var_name, var_type in cls.__annotations__.items():
class Checker(TypeChecker):
required_type = var_type
setattr(cls, var_name, Checker(var_name))
return cls
class TypeCheckMeta(type):
def __new__(meta, name, bases, dct):
cls = super().__new__(meta, name, bases, dct)
return type_check(cls)
class Base(metaclass=TypeCheckMeta):
__annotations__ = {}
class Point(Base):
x: int
y: int
def __init__(self, x, y):
self.x = x
self.y = y
def move_by(self, dx, dy):
self.x += dx
self.y += dy
def __str__(self):
return f'A Point at {self.x}, {self.y}'
def __repr__(self):
return f'{self.__class__.__name__}({self.x}, {self.y})'
class Circle(Base):
center: Point
radius: int
def __init__(self, center, radius):
self.center = center
self.radius = radius
@property
def area(self):
return pi * self.radius ** 2
def __str__(self):
return f'A Circle at {self.center.x}, {self.center.y} and ' + \
f'radius {self.radius}'
def __repr__(self):
return f'{self.__class__.__name__}({self.center!r}, {self.radius!r})'