Python 中的魔法方法

Python 中的对象都有诸如 __init__() 这样的方法，它们都有各自特定的用途，却
无法直接被调用。虽然无法被直接调用，实际上你却经常在使用这些方法，比如创建对象实例式
就调用了 __new__() 和 __init__ 方法。那么这些魔法方法还有那些其它的有趣用法呢？

操作符重载

Python 中的操作符运算实际上都是在隐式地调用这些魔法方法，如果你重写了对应的魔法方法，
就能修改操作符的运算规则。比如，逻辑或操作符 | 对应了魔法方法 __ror__，
因此我们可以重载 __ror__ 来实现类似 Shell 中的管道：

  1. class Pipe(object):
  2.     def __init__(self, func):
  3.         self.func = func
  5.     def __ror__(self, other):
  6.         def generator():
  7.             for obj in other:
  8.                 if obj is not None:
  9.                     yield self.func(obj)
  10.         return generator()
  12. @Pipe
  13. def even_filter(num):
  14.     return num if num % 2 == 0 else None
  16. @Pipe
  17. def multiply_by_three(num):
  18.     return num*3
  20. @Pipe
  21. def convert_to_string(num):
  22.     return 'The Number: %s' % num
  24. @Pipe
  25. def echo(item):
  26.     print item
  27.     return item
  29. def force(sqs):
  30.     for item in sqs: pass
  32. nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  34. force(nums | even_filter | multiply_by_three | convert_to_string | echo)

（代码出自酷壳网友）

这里有张详细的对照表：

  1. Binary Operators
  2. Operator    Method
  3. +   object.__add__(self, other)
  4. -   object.__sub__(self, other)
  5. *   object.__mul__(self, other)
  6. //  object.__floordiv__(self, other)
  7. /   object.__div__(self, other)
  8. %   object.__mod__(self, other)
  9. **  object.__pow__(self, other[, modulo])
  10. <<  object.__lshift__(self, other)
  11. >>  object.__rshift__(self, other)
  12. &   object.__and__(self, other)
  13. ^   object.__xor__(self, other)
  14. |   object.__or__(self, other)
  16. Extended Assignments
  17. Operator    Method
  18. +=  object.__iadd__(self, other)
  19. -=  object.__isub__(self, other)
  20. *=  object.__imul__(self, other)
  21. /=  object.__idiv__(self, other)
  22. //= object.__ifloordiv__(self, other)
  23. %=  object.__imod__(self, other)
  24. **= object.__ipow__(self, other[, modulo])
  25. <<= object.__ilshift__(self, other)
  26. >>= object.__irshift__(self, other)
  27. &=  object.__iand__(self, other)
  28. ^=  object.__ixor__(self, other)
  29. |=  object.__ior__(self, other)
  31. Unary Operators
  32. Operator    Method
  33. -   object.__neg__(self)
  34. +   object.__pos__(self)
  35. abs()   object.__abs__(self)
  36. ~   object.__invert__(self)
  37. complex()   object.__complex__(self)
  38. int()   object.__int__(self)
  39. long()  object.__long__(self)
  40. float() object.__float__(self)
  41. oct()   object.__oct__(self)
  42. hex()   object.__hex__(self
  44. Comparison Operators
  45. Operator    Method
  46. <   object.__lt__(self, other)
  47. <=  object.__le__(self, other)
  48. ==  object.__eq__(self, other)
  49. !=  object.__ne__(self, other)
  50. >=  object.__ge__(self, other)
  51. >   object.__gt__(self, other)

参考：Magic Methods and Operator Overloading