1. Item 27: classmethod

    class A(object):
        value = 5
        @classmethod
        def cls_fun(cls):
            print('A.cls_fun', cls, cls.value)
        def fun(self):
            print('A.fun', self, self.value)
            self.cls_fun()
    class B(A):
        value = 10
    class C(A):
        value = 15
        @classmethod
        def cls_fun(cls):
            print('B.cls_fun', cls, cls.value)
        def fun2(self):
            print …

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  2. Item 26: staticmethod

    class A(object):
        @staticmethod
        def static_fun():
            print('A.static_fun')
    
        def fun(self):
            print('A.fun', self)
            print('#', end='')
            self.static_fun()
    
    class B(A):
        @staticmethod
        def static_fun():
            print('B.static_fun')
    
        def fun2(self):
            print('B.fun2', self)
            print('#', end='')
            self.static_fun()
    
    a = A(); a.static_fun(); a.fun()
    print('----')
    b = B(); b …

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  3. Item 25: Metaclass

    class Field(object):
        def __get__(self, instance, owner):
            print('__get__', self, instance, self.name)
            return getattr(instance, self.name)
        def __set__(self, instance, value):
            print('__set__', self, instance, self.name, value)
            setattr(instance, self.name, value)
    
    class Meta(type):
        def __new__(meta, name, bases, class_dict):
            print('__new__', name, bases, class_dict …

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  4. Item 24: List

    k = 3
    x = [0] * k
    y = [[0] * k] * k
    z = [[0] * k for i in range(k)]
    
    print(x, y, z)
    
    x[0] = 1
    x[1] = 2
    
    y[0][0] = 1
    y[0][1] = 2
    
    z[0][0] = 1
    z[0][1] = 2
    
    print(x, y, z)
    

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  5. Item 23: getattribute

    class A(object):
        def __init__(self):
            self.x = 5
    
        def __getattr__(self, name):
            print('    A.__getattr__', self, name)
            if name and name[0].isalpha():
                setattr(self, name, 10)
                return 10
            raise AttributeError('cannot get ' + name)
    
    class B(A):
        def __getattribute__(self, name):
            print('    B.__getattribute__', self, name)
            if name == 'z …

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  6. Item 22: getattr and setattr

    class A(object):
        def __init__(self):
            self.x = 5
        def __getattr__(self, name):
            print('A.__getattr__(', self, ',', name, ')')
            setattr(self, name, 10)
            return 10
        def __setattr__(self, name, value):
            print('A.__setattr__(', self, ',', name, ',', value, ')')
            self.__dict__[name] = value
    
    a = A()
    print('P1:', a.x)
    print('P2:', a.x)
    a …

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  7. Item 21: Descriptors

    class Field(object):
        def __init__(self, name):
            self.name = '__' + name
        def __get__(self, instance, owner):
            print('__get__', self, instance, owner)
            return getattr(instance, self.name)
        def __set__(self, instance, value):
            print('__set__', self, instance, value)
            setattr(instance, self.name, value)
    
    class Record(object):
        a = Field('a')
        b = Field('b …

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  8. Item 20: for Loop Variable

    a = 0
    for x in range(3):
        a += 1
    
    b = 0
    for y in range(5):
        for z in range(8):
            b += 1
    
    c = 0
    for w in range(13):
        for w in range(23):
            c += 1
    
    print(x, y, z, w)
    print(a, b, c)
    

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  9. Item 19: Class Property

    class Temperature(object):
        def __init__(self, celsius):
            self.celsius = celsius
    
        def get_fahrenheit(self):
            return self.celsius / 5 * 9 + 32
    
        def set_fahrenheit(self, fahrenheit):
            self.celsius = (fahrenheit - 32) / 9 * 5
    
        fahrenheit = property(get_fahrenheit, set_fahrenheit)
    
    t = Temperature(30)
    print(t.celsius, t.fahrenheit)
    t.fahrenheit = 50
    print(t.celsius, t.fahrenheit)
    

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  10. Item 18: Class and dict attribute

    class Point(object):
        def __init__(self, x, y):
            self.x = x
            self.y = y
    class GoodPoint(object):
        __slots__ = ('x', 'y')
        def __init__(self, x, y):
            self.x = x
            self.y = y
    
    for point_type in (Point, GoodPoint):
        print('----', point_type)
        p = point_type(1, 2)
        try:
            p.z = 3
        except AttributeError as e …

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