简化数据结构的初始化

可以在一个基类中写一个公用的 __init__() 函数：

import math

class Structure1:
    # Class variable that specifies expected fields
    _fields = []

    def __init__(self, *args):
        if len(args) != len(self._fields):
            raise TypeError('Expected {} arguments'.format(len(self._fields)))
        # Set the arguments
        for name, value in zip(self._fields, args):
            setattr(self, name, value)
然后使你的类继承自这个基类:

# Example class definitions
class Stock(Structure1):
    _fields = ['name', 'shares', 'price']

class Point(Structure1):
    _fields = ['x', 'y']

class Circle(Structure1):
    _fields = ['radius']

    def area(self):
        return math.pi * self.radius ** 2
使用这些类的示例：

>>> s = Stock('ACME', 50, 91.1)
>>> p = Point(2, 3)
>>> c = Circle(4.5)
>>> s2 = Stock('ACME', 50)
Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "structure.py", line 6, in __init__
        raise TypeError('Expected {} arguments'.format(len(self._fields)))
TypeError: Expected 3 arguments
如果还想支持关键字参数，可以将关键字参数设置为实例属性：

class Structure2:
    _fields = []

    def __init__(self, *args, **kwargs):
        if len(args) > len(self._fields):
            raise TypeError('Expected {} arguments'.format(len(self._fields)))

        # Set all of the positional arguments
        for name, value in zip(self._fields, args):
            setattr(self, name, value)

        # Set the remaining keyword arguments
        for name in self._fields[len(args):]:
            setattr(self, name, kwargs.pop(name))

        # Check for any remaining unknown arguments
        if kwargs:
            raise TypeError('Invalid argument(s): {}'.format(','.join(kwargs)))
# Example use
if __name__ == '__main__':
    class Stock(Structure2):
        _fields = ['name', 'shares', 'price']

    s1 = Stock('ACME', 50, 91.1)
    s2 = Stock('ACME', 50, price=91.1)
    s3 = Stock('ACME', shares=50, price=91.1)
    # s3 = Stock('ACME', shares=50, price=91.1, aa=1)
你还能将不在 _fields 中的名称加入到属性中去：

class Structure3:
    # Class variable that specifies expected fields
    _fields = []

    def __init__(self, *args, **kwargs):
        if len(args) != len(self._fields):
            raise TypeError('Expected {} arguments'.format(len(self._fields)))

        # Set the arguments
        for name, value in zip(self._fields, args):
            setattr(self, name, value)

        # Set the additional arguments (if any)
        extra_args = kwargs.keys() - self._fields
        for name in extra_args:
            setattr(self, name, kwargs.pop(name))

        if kwargs:
            raise TypeError('Duplicate values for {}'.format(','.join(kwargs)))

# Example use
if __name__ == '__main__':
    class Stock(Structure3):
        _fields = ['name', 'shares', 'price']

    s1 = Stock('ACME', 50, 91.1)
    s2 = Stock('ACME', 50, 91.1, date='8/2/2012')