3.3.8. 模拟数值类型 ¶

可以定义下列方法，以模拟数值对象。特定种类数字实现 (如：非整数按位操作) 不支持的对应操作方法，应保持未定义。

对象。 __add__ ( self , other ) ¶

对象。 __sub__ ( self , other ) ¶

对象。 __mul__ ( self , other ) ¶

对象。 __matmul__ ( self , other ) ¶

对象。 __truediv__ ( self , other ) ¶

对象。 __floordiv__ ( self , other ) ¶

对象。 __mod__ ( self , other ) ¶

对象。 __divmod__ ( self , other ) ¶

对象。 __pow__ ( self , other [ , 模 ] ) ¶

对象。 __lshift__ ( self , other ) ¶

对象。 __rshift__ ( self , other ) ¶

对象。 __and__ ( self , other ) ¶

对象。 __xor__ ( self , other ) ¶

对象。 __or__ ( self , other ) ¶

调用这些方法能实现二进制算术运算 ( + , - , * , @ , / , // , % , divmod() , pow() , ** , << , >> , & , ^ , | )。例如，要评估表达式 x + y ，其中 x 是实例化的类拥有 __add__() 方法， type(x).__add__(x, y) 被调用。 __divmod__() 方法应该是相当于使用 __floordiv__() and __mod__() ; it should not be related to __truediv__() 。注意， __pow__() should be defined to accept an optional third argument if the ternary version of the built-in pow() function is to be supported.

If one of those methods does not support the operation with the supplied arguments, it should return NotImplemented .

对象。 __radd__ ( self , other ) ¶

对象。 __rsub__ ( self , other ) ¶

对象。 __rmul__ ( self , other ) ¶

对象。 __rmatmul__ ( self , other ) ¶

对象。 __rtruediv__ ( self , other ) ¶

对象。 __rfloordiv__ ( self , other ) ¶

对象。 __rmod__ ( self , other ) ¶

对象。 __rdivmod__ ( self , other ) ¶

对象。 __rpow__ ( self , other [ , 模 ] ) ¶

对象。 __rlshift__ ( self , other ) ¶

对象。 __rrshift__ ( self , other ) ¶

对象。 __rand__ ( self , other ) ¶

对象。 __rxor__ ( self , other ) ¶

对象。 __ror__ ( self , other ) ¶

调用这些方法能实现二进制算术运算 ( + , - , * , @ , / , // , % , divmod() , pow() , ** , << , >> , & , ^ , | ) with reflected (swapped) operands. These functions are only called if the left operand does not support the corresponding operation [ 3 ] and the operands are of different types. [ 4 ] 例如，要评估表达式 x - y ，其中 y 是实例化的类拥有 __rsub__() 方法， type(y).__rsub__(y, x) is called if type(x).__sub__(x, y) 返回 NotImplemented .

注意，三次 pow() 不会试着调用 __rpow__() (强制转换规则会变得过于复杂)。

注意

If the right operand’s type is a subclass of the left operand’s type and that subclass provides a different implementation of the reflected method for the operation, this method will be called before the left operand’s non-reflected method. This behavior allows subclasses to override their ancestors’ operations.

对象。 __iadd__ ( self , other ) ¶

对象。 __isub__ ( self , other ) ¶

对象。 __imul__ ( self , other ) ¶

对象。 __imatmul__ ( self , other ) ¶

对象。 __itruediv__ ( self , other ) ¶

对象。 __ifloordiv__ ( self , other ) ¶

对象。 __imod__ ( self , other ) ¶

对象。 __ipow__ ( self , other [ , 模 ] ) ¶

对象。 __ilshift__ ( self , other ) ¶

对象。 __irshift__ ( self , other ) ¶

对象。 __iand__ ( self , other ) ¶

对象。 __ixor__ ( self , other ) ¶

对象。 __ior__ ( self , other ) ¶

These methods are called to implement the augmented arithmetic assignments ( += , -= , *= , @= , /= , //= , %= , **= , <<= , >>= , &= , ^= , |= ). These methods should attempt to do the operation in-place (modifying self ) and return the result (which could be, but does not have to be, self ). If a specific method is not defined, or if that method returns NotImplemented , the augmented assignment falls back to the normal methods. For instance, if x is an instance of a class with an __iadd__() 方法， x += y 相当于 x = x.__iadd__(y) 。若 __iadd__() does not exist, or if x.__iadd__(y) 返回 NotImplemented , x.__add__(y) and y.__radd__(x) are considered, as with the evaluation of x + y . In certain situations, augmented assignment can result in unexpected errors (see Why does a_tuple[i] += [‘item’] raise an exception when the addition works? ), but this behavior is in fact part of the data model.

对象。 __neg__ ( self ) ¶

对象。 __pos__ ( self ) ¶

对象。 __abs__ ( self ) ¶

对象。 __invert__ ( self ) ¶

被调用以实现一元算术运算 ( - , + , abs() and ~ ).

对象。 __complex__ ( self ) ¶

对象。 __int__ ( self ) ¶

对象。 __float__ ( self ) ¶

Called to implement the built-in functions complex() , int() and float() . Should return a value of the appropriate type.

对象。 __index__ ( self ) ¶

Called to implement operator.index() , and whenever Python needs to losslessly convert the numeric object to an integer object (such as in slicing, or in the built-in bin() , hex() and oct() functions). Presence of this method indicates that the numeric object is an integer type. Must return an integer.

若 __int__() , __float__() and __complex__() are not defined then corresponding built-in functions int() , float() and complex() fall back to __index__() .

对象。 __round__ ( self [ , ndigits ] ) ¶

对象。 __trunc__ ( self ) ¶

对象。 __floor__ ( self ) ¶

对象。 __ceil__ ( self ) ¶

Called to implement the built-in function round() and math 函数 trunc() , floor() and ceil() . Unless ndigits 被传递给 __round__() all these methods should return the value of the object truncated to an Integral (typically an int ).

内置函数 int() falls back to __trunc__() if neither __int__() nor __index__() 有定义。

3.11 版改变： The delegation of int() to __trunc__() 被弃用。

>>> class C:
...     pass
...
>>> c = C()
>>> c.__len__ = lambda: 5
>>> len(c)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: object of type 'C' has no len()
																											

>>> 1 .__hash__() == hash(1)
True
>>> int.__hash__() == hash(int)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: descriptor '__hash__' of 'int' object needs an argument
																											

>>> type(1).__hash__(1) == hash(1)
True
>>> type(int).__hash__(int) == hash(int)
True
																											

>>> class Meta(type):
...     def __getattribute__(*args):
...         print("Metaclass getattribute invoked")
...         return type.__getattribute__(*args)
...
>>> class C(object, metaclass=Meta):
...     def __len__(self):
...         return 10
...     def __getattribute__(*args):
...         print("Class getattribute invoked")
...         return object.__getattribute__(*args)
...
>>> c = C()
>>> c.__len__()                 # Explicit lookup via instance
Class getattribute invoked
10
>>> type(c).__len__(c)          # Explicit lookup via type
Metaclass getattribute invoked
10
>>> len(c)                      # Implicit lookup
10
																											

class Reader:
    async def readline(self):
        ...
    def __aiter__(self):
        return self
    async def __anext__(self):
        val = await self.readline()
        if val == b'':
            raise StopAsyncIteration
        return val
																											

class AsyncContextManager:
    async def __aenter__(self):
        await log('entering context')
    async def __aexit__(self, exc_type, exc, tb):
        await log('exiting context')