Python3 操作符重载方法示例

基础知识

实际上，“运算符重载”只是意味着在类方法中拦截内置的操作……当类的实例出现在内置操作中，Python自动调用你的方法，并且你的方法的返回值变成了相应操作的结果。以下是对重载的关键概念的复习：

1. 运算符重载让类拦截常规的Python运算。
2. 类可重载所有Python表达式运算符
3. 类可以重载打印、函数调用、属性点号运算等内置运算
4. 重载使类实例的行为像内置类型。
5. 重载是通过特殊名称的类方法来实现的。

换句话说，当类中提供了某个特殊名称的方法，在该类的实例出现在它们相关的表达式时，Python自动调用它们。正如我们已经学习过的，运算符重载方法并非必须的，并且通常也不是默认的；如果你没有编写或继承一个运算符重载方法，只是意味着你的类不会支持相应的操作。然而，当使用的时候，这些方法允许类模拟内置对象的接口，因此表现得更一致。

以下代码以Python3.6.1为例

操作符重载方法: 类(class)通过使用特殊名称的方法(len(self))来实现被特殊语法(len())的调用

#coding=utf-8
# specialfuns.py 操作符重载方法
# 类(class)通过使用特殊名称的方法(__len__(self))来实现被特殊语法(len())的调用

# 构造 与 析构 方法
class demo1:

  # 构造方法, 对象实例化时调用
  def __init__(self):
    print("构造方法")

  # 析构方法, 对象被回收时调用
  def __del__(self):
    print("析构方法")

# new
class demo2(object):
  # __init__之前调用, 一般用于重写父类的__new__方法, 具体使用见 类 文章的 元类 代码部分(http://blog.csdn.net/rozol/article/details/69317339)
  def __new__(cls):
    print("new")
    return object.__new__(cls)

# 算术运算
class demo3:
  def __init__(self, num):
    self.data = num
  # +
  def __add__(self, other):
    return self.data + other.data
  # -
  def __sub__(self, other):
    return self.data - other.data
  # *
  def __mul__(self, other):
    return self.data * other.data
  # /
  def __truediv__(self, other):
    return self.data / other.data
  # //
  def __floordiv__(self, other):
    return self.data // other.data
  # %
  def __mod__(self, other):
    return self.data % other.data
  # divmod()
  def __divmod__(self, other):
    # 商(10/5),余数(10%5)
    return self.data / other.data, self.data % other.data
  # **
  def __pow__(self, other):
    return self.data ** other.data
  # <<
  def __lshift__(self, other):
    return self.data << other.data
  # >>
  def __rshift__(self, other):
    return self.data >> other.data
  # &
  def __and__(self, other):
    return self.data & other.data
  # ^
  def __xor__(self, other):
    return self.data ^ other.data
  # |
  def __or__(self, other):
    return self.data | other.data

class none:
  def __init__(self, num):
    self.data = num
# 反算术运算符(a+b, 若a不支持算术运算符,则寻找b的算术运算符)(注:位置变换, 在原始函数名前+r)
class demo4:
  def __init__(self, num):
    self.data = num
  # +
  def __radd__(self, other):
    return other.data + self.data
  # -
  def __rsub__(self, other):
    return other.data - self.data
  # *
  def __rmul__(self, other):
    return other.data * self.data
  # /
  def __rtruediv__(self, other):
    return other.data / self.data
  # //
  def __rfloordiv__(self, other):
    return other.data // self.data
  # %
  def __rmod__(self, other):
    return other.data % self.data
  # divmod()
  def __rdivmod__(self, other):
    return other.data / self.data, other.data % self.data
  # **
  def __rpow__(self, other):
    return other.data ** self.data
  # <<
  def __rlshift__(self, other):
    return other.data << self.data
  # >>
  def __rrshift__(self, other):
    return other.data >> self.data
  # &
  def __rand__(self, other):
    return other.data & self.data
  # ^
  def __rxor__(self, other):
    return other.data ^ self.data
  # |
  def __ror__(self, other):
    return other.data | self.data

# 增量赋值运算,(注:位置同原始函数,在原始函数名前+i)
class demo5():
  def __init__(self, num):
    self.data = num
  # +=
  def __iadd__(self, other):
    return self.data + other
  # -=
  def __isub__(self, other):
    return self.data - other
  # *=
  def __imul__(self, other):
    return self.data * other
  # /=
  def __itruediv__(self, other):
    return self.data / other
  # //=
  def __ifloordiv__(self, other):
    return self.data // other
  # %=
  def __imod__(self, other):
    return self.data % other
  # **=
  def __ipow__(self, other):
    return self.data ** other
  # <<=
  def __ilshift__(self, other):
    return self.data << other
  # >>=
  def __irshift__(self, other):
    return self.data >> other
  # &=
  def __iand__(self, other):
    return self.data & other
  # ^=
  def __ixor__(self, other):
    return self.data ^ other
  # |=
  def __ior__(self, other):
    return self.data | other

# 比较运算符
class demo6:
  def __init__(self, num):
    self.data = num
  # <
  def __lt__(self, other):
    return self.data < other.data
  # <=
  def __le__(self, other):
    return self.data <= other.data
  # ==
  def __eq__(self, other):
    return self.data == other.data
  # !=
  def __ne__(self, other):
    return self.data != other.data
  # >
  def __gt__(self, other):
    return self.data > other.data
  # >=
  def __ge__(self, other):
    return self.data >= other.data

# 一元操作符
class demo7:
  def __init__(self, num):
    self.data = num
  # + 正号
  def __pos__(self):
    return +abs(self.data)
  # - 负号
  def __neg__(self):
    return -abs(self.data)
  # abs() 绝对值
  def __abs__(self):
    return abs(self.data)
  # ~ 按位取反
  def __invert__(self):
    return ~self.data
  # complex() 字符转数字
  def __complex__(self):
    return 1+2j
  # int() 转为整数
  def __int__(self):
    return 123
  # float() 转为浮点数
  def __float__(self):
    return 1.23
  # round() 近似值
  def __round__(self):
    return 1.123

# 格式化
class demo8:
  # print() 打印
  def __str__(self):
    return "This is the demo."
  # repr() 对象字符串表示
  def __repr__(self):
    return "This is a demo."
  # bytes() 对象字节字符串表现形式
  def __bytes__(self):
    return b"This is one demo."
  # format() 格式化
  def __format__(self, format_spec):
    return self.__str__()

# 属性访问
class demo9:
  # 获取(不存在)属性
  def __getattr__(self):
    print ("访问的属性不存在")
  # getattr() hasattr() 获取属性
  def __getattribute__(self, attr):
    print ("访问的属性是%s"%attr)
    return attr
  # setattr() 设置属性
  def __setattr__(self, attr, value):
    print ("设置 %s 属性值为 %s"%(attr, value))
  # delattr() 删除属性
  def __delattr__(self, attr):
    print ("删除 %s 属性"%attr)

# ===================================================================
# 描述器(类(test1)的实例出现在属主类(runtest)中,这些方法才会调用)(注:函数调用,这些方法不会被调用)
class test1:
  def __init__(self, value = 1):
    self.value = value * 2
  def __set__(self, instance, value):
    print("set %s %s %s"%(self, instance, value))
    self.value = value * 2
  def __get__(self, instance, owner):
    print("get %s %s %s"%(self, instance, owner))
    return self.value
  def __delete__(self, instance):
    print("delete %s %s"%(self, instance))
    del self.value

class test2:
  def __init__(self, value = 1):
    self.value = value + 0.3
  def __set__(self, instance, value):
    print("set %s %s %s"%(self, instance, value))
    instance.t1 = value + 0.3
  def __get__(self, instance, owner):
    print("get %s %s %s"%(self, instance, owner))
    return instance.t1
  def __delete__(self, instance):
    print("delete %s %s"%(self, instance))
    del self.value

class runtest:
  t1 = test1()
  t2 = test2()

# ---

# 自定义property
class property_my:
  def __init__(self, fget=None, fset=None, fdel=None):
    self.fget = fget
    self.fset = fset
    self.fdel = fdel
  # 对象被获取(self自身, instance调用该对象的对象(demo9), owner调用该对象的对象类对象(demo9))
  def __get__(self, instance, owner):
    print("get %s %s %s"%(self, instance, owner))
    return self.fget(instance)
  # 对象被设置属性时
  def __set__(self, instance, value):
    print("set %s %s %s"%(self, instance, value))
    self.fset(instance, value)
  # 对象被删除时
  def __delete__(self, instance):
    print("delete %s %s"%(self, instance))
    self.fdel(instance)

class demo10:
  def __init__(self):
    self.num = None
  def setvalue(self, value):
    self.num = value
  def getvalue(self):
    return self.num
  def delete(self):
    del self.num
  x = property_my(getvalue, setvalue, delete)

# ===================================================================

# 自定义容器
class lis:
  def __init__(self, *args):
    self.lists = args
    self.size = len(args)
    self.startindex = 0
    self.endindex = self.size
  # len() 容器元素数量
  def __len__(self):
    return self.size;
  # lis[1] 获取元素
  def __getitem__(self, key = 0):
    return self.lists[key]
  # lis[1] = value 设置元素
  def __setitem__(self, key, value):
    pass
  # del lis[1] 删除元素
  def __delitem__(self, key):
    pass
  # 返回迭代器
  def __iter__(self):
    return self
  # rversed() 反向迭代器
  def __reversed__(self):
    while self.endindex > 0:
      self.endindex -= 1
      yield self[self.endindex]
  # next() 迭代器下个元素
  def __next__(self):
    if self.startindex >= self.size:
      raise StopIteration # 控制迭代器结束

    elem = self.lists[self.startindex]
    self.startindex += 1
    return elem

  # in / not in
  def __contains__(self, item):
    for i in self.lists:
      if i == item:
        return True
    return False

# yield 生成器(执行一次返回,下次继续执行后续代码返回)
def yielddemo():
  num = 0
  while 1: # 1 == True; 0 == False
    if num >= 10:
      raise StopIteration
    num += 1
    yield num

# 能接收数据的生成器
def yielddemo_1():
  while 1:
    num = yield
    print(num)

# with 自动上下文管理
class withdemo:
  def __init__(self, value):
    self.value = value
  # 返回值为 as 之后的值
  def __enter__(self):
    return self.value
  # 执行完成,退出时的数据清理动作
  def __exit__(self, exc_type, exc_value, traceback):
    del self.value

if __name__ == "__main__":
  # 构造与析构
  d1 = demo1()
  del d1

  # new
  d2 = demo2()

  # 算术运算符
  d3 = demo3(3)
  d3_1 = demo3(5)
  print(d3 + d3_1)
  print(d3 - d3_1)
  print(d3 * d3_1)
  print(d3 / d3_1)
  print(d3 // d3_1)
  print(d3 % d3_1)
  print(divmod(d3, d3_1))
  print(d3 ** d3_1)
  print(d3 << d3_1)
  print(d3 >> d3_1)
  print(d3 & d3_1)
  print(d3 ^ d3_1)
  print(d3 | d3_1)

  # 反运算符
  d4 = none(3)
  d4_1 = demo4(5)
  print(d4 + d4_1)
  print(d4 - d4_1)
  print(d4 * d4_1)
  print(d4 / d4_1)
  print(d4 // d4_1)
  print(d4 % d4_1)
  print(divmod(d4, d4_1))
  print(d4 ** d4_1)
  print(d4 << d4_1)
  print(d4 >> d4_1)
  print(d4 & d4_1)
  print(d4 ^ d4_1)
  print(d4 | d4_1)

  # 增量赋值运算(测试时注释其他代码)
  d5 = demo5(3)
  d5 <<= 5
  d5 >>= 5
  d5 &= 5
  d5 ^= 5
  d5 |= 5
  d5 += 5
  d5 -= 5
  d5 *= 5
  d5 /= 5
  d5 //= 5
  d5 %= 5
  d5 **= 5
  print(d5)

  # 比较运算符
  d6 = demo6(3)
  d6_1 = demo6(5)
  print(d6 < d6_1)
  print(d6 <= d6_1)
  print(d6 == d6_1)
  print(d6 != d6_1)
  print(d6 > d6_1)
  print(d6 >= d6_1)

  # 一元操作符(测试时注释其他代码)
  d7 = demo7(-5)
  num = +d7
  num = -d7
  num = abs(d7)
  num = ~d7
  print(num)
  print(complex(d7))
  print(int(d7))
  print(float(d7))
  print(round(d7))

  # 格式化
  d8 = demo8()
  print(d8)
  print(repr(d8))
  print(bytes(d8))
  print(format(d8, ""))

  # 属性访问
  d9 = demo9()
  setattr(d9, "a", 1) # => 设置 a 属性值为 1
  print(getattr(d9, "a")) # => a / 访问的属性是a
  print(hasattr(d9, "a")) # => True / 访问的属性是a
  delattr(d9, "a") # 删除 a 属性
  # ---
  d9.x = 100 # => 设置 x 属性值为 100
  print(d9.x) # => x / 访问的属性是x
  del d9.x # => 删除 x 属性

  # 描述器
  r = runtest()
  r.t1 = 100 # => <__main__.test1> <__main__.runtest> 100
  print(r.t1) # => 200 / <__main__.test1> <__main__.runtest> <class '__main__.runtest'>
  del r.t1 # => <__main__.test1> <__main__.runtest>
  r.t2 = 200 # => <__main__.test2> <__main__.runtest> 200 / <__main__.test1> <__main__.runtest> 200.3
  print(r.t2) # => 400.6 / <__main__.test2> <__main__.runtest> <class '__main__.runtest'> / <__main__.test1> <__main__.runtest> <class '__main__.runtest'>
  del r.t2 # <__main__.test2> <__main__.runtest>
  # ---
  # 自定义property
  d10 = demo10()
  d10.x = 100; # => <__main__.property_my> <__main__.demo10> 100
  print(d10.x) # => 100 / <__main__.property_my> <__main__.demo10> <class '__main__.demo10'>
  del d10.x # => <__main__.property_my> <__main__.demo10>
  d10.num = 200;
  print(d10.num) # => 200
  del d10.num

  # 自定义容器(迭代器Iterator)
  lis = lis(1,2,3,4,5,6)
  print(len(lis))
  print(lis[1])
  print(next(lis))
  print(next(lis))
  print(next(lis))
  for i in lis:
    print (i)
  for i in reversed(lis):
    print (i)
  print(3 in lis)
  print(7 in lis)
  print(3 not in lis)
  print(7 not in lis)

  # yield 生成器(可迭代对象Iterable)
  for i in yielddemo():
    print (i)
  # ---
  iters = iter(yielddemo())
  print(next(iters))
  print(next(iters))

  # --- 发送数据给生成器 ---
  iters = yielddemo_1()
  next(iters)
  iters.send(6) # 发送数据并执行
  iters.send(10)

  # with 自动上下文管理
  with withdemo("Less is more!") as s:
    print(s)

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