J

#### John Ladasky

I am awaiting my approval to join the numpy-discussion mailing list, at scipy.org. I realize that would be the best place to ask my question. However, numpy is so widely used, I figure that someone here would be able to help.

I like to use numpy.where() to select parts of arrays. I have encountered what I would consider to be a bug when you try to use where() in conjunction with the multiple comparison syntax of Python. Here's a minimal example:

Python 3.3.2+ (default, Oct 9 2013, 14:50:09)

[GCC 4.8.1] on linux

Type "help", "copyright", "credits" or "license" for more information.

Traceback (most recent call last):import numpy as np

a = np.arange(10)

a array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])

b = np.where(a < 5)

b (array([0, 1, 2, 3, 4]),)

c = np.where(2 < a < 7)

File "<stdin>", line 1, in <module>

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

Defining b works as I want and expect. The array contains the indices (notthe values) of a where a < 5.

For my definition of c, I expect (array([3, 4, 5, 6]),). As you can see, Iget a ValueError instead. I have seen the error message about "the truth value of an array with more than one element" before, and generally I understand how I (accidentally) provoke it. This time, I don't see it. In defining c, I expect to be stepping through a, one element at a time, just as Idid when defining b.

Does anyone understand why this happens? Is there a smart work-around? Thanks.