python - 在python中为任何对象创建无穷大和负无穷大

Question

我正在开发一个库，该库实现了一种适用于任何有序数据类型的数据结构——范围集。当您允许正无穷大和负无穷大时，许多操作(如反转)会变得有趣。

一个目标是让日期时间对象与这个模块一起工作，为了支持非数字对象的无穷大，我创建了 INFINITY 和 NEGATIVE_INFINITY:

class _Indeterminate(object):
    def __eq__(self, other):
        return other is self

@functools.total_ordering
class _Infinity(_Indeterminate):
    def __lt__(self, other):
        return False
    def __gt__(self, other):
        return True
    def __str__(self):
        return 'inf'
    __repr__ = __str__

@functools.total_ordering
class _NegativeInfinity(_Indeterminate):
    def __lt__(self, other):
        return True
    def __gt__(self, other):
        return False
    def __str__(self):
        return '-inf'

INFINITY = _Infinity()
NEGATIVE_INFINITY = _NegativeInfinity()

不幸的是，这对位于 cmp() 操作左侧的日期时间对象不起作用:

In [1]: from rangeset import *
In [2]: from datetime import datetime
In [3]: now = datetime.now()
In [4]: cmp(INFINITY, now)
Out[4]: 1
In [5]: cmp(now, INFINITY)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
/home/axiak/Documents/rangeset/<ipython-input-5-c928d3687d92> in <module>()
----> 1 cmp(now, INFINITY)

TypeError: can't compare datetime.datetime to _Infinity

我曾希望我可以通过使用 cmp 包装器来绕过这个限制，它只确保我的对象总是被调用，但我真的想使用 .sort() 方法，这将导致 cmp在这些对象之间调用。

有没有办法创建一个真正小于任何其他对象，真正大于任何其他对象的对象？

模块主页:https://github.com/axiak/py-rangeset

Answer 1

来自 docs

In order to stop comparison from falling back to the default scheme of comparing object addresses, date comparison normally raises TypeError if the other comparand isn’t also a date object. However, NotImplemented is returned instead if the other comparand has a timetuple() attribute.

因此为了允许与日期时间对象进行比较，添加一个timetuple 方法，例如

class _Infinity(object):

    def __lt__(self, other):
        return False

    def __gt__(self, other):
        return True

    def timetuple(self):
        return tuple()

import datetime
INF = _Infinity()
now = datetime.datetime.now()
print cmp(INF, now)
print cmp(now, INF)

输出:

1    
-1