initial

Author: fpierfed

08-interlude_metaclasses.py

@@ -0,0 +1,26 @@
+class Meta(type):
+    def __new__(meta, name, bases, dct):
+        result = super().__new__(meta, name, bases, dct)
+        print(f'Called: __new__({meta}, {name}, {bases}, {dct} -> {result}')
+        return result
+
+    def __init__(cls, name, bases, dct):
+        result = super().__init__(name, bases, dct)
+        print(f'Called: __init__({cls}, {name}, {bases}, {dct} -> {result}')
+        return result
+
+
+class Point(object, metaclass=Meta):
+    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})'

09-metaclasses.py

@@ -0,0 +1,74 @@
+from math import pi
+
+
+class TypeChecker:
+    required_type = object
+
+    def __init__(self, name=None):
+        self.name = 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})'