python-2.7 - 为什么链式(间隔)比较不适用于 numpy 数组？

Question

a < b < c是 chained expression在 Python 中，看起来它适用于定义了适当比较运算符的对象，但它不适用于 numpy 数组。为什么？

import numpy as np

class ContrarianContainer(object):
    def __init__(self, x):
        self.x = x
    def __le__(self, y):
        return not self.x <= y
    def __lt__(self, y):
        return not self.x < y
    def __ge__(self, y):
        return not self.x >= y
    def __gt__(self, y):
        return not self.x > y
    def __eq__(self, y):
        return not self.x == y
    def __ne__(self, y):
        return not self.x != y

numlist = np.array([1,2,3,4])
for n in numlist:
    print 0 < n < 3.5
for n in numlist:
    print 0 > ContrarianContainer(n) > 3.5
print 0 < numlist < 3.5

这打印:

True
True
True
False
True
True
True
False
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-187-277da7750148> in <module>()
      4 for n in numlist:
      5     print 0 < n < 3.5
----> 6 print 0 < numlist < 3.5

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Answer 1

0 < numlist < 3.5

相当于:

(0 < numlist) and (numlist < 3.5)

除了 numlist只评估一次。

隐式 and两个结果之间导致错误