Re: Rich Comparisons Gotcha

Robert Kern wrote:
James Stroud wrote:
py> 112 = [1, y]
py> y in 112
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: The truth value of an array with more than one element is...

but not

py> ll1 = [y,1]
py> y in ll1
True

It's this discrepancy that seems like a bug, not that a ValueError is raised in the former case, which is perfectly reasonable to me.

Nothing to do with numpy. list.__contains__() checks for identity with "is" before it goes to __eq__().

....but only for the first element of the list:

py> import numpy
py> y = numpy.array([1,2,3])
py> y
array([1, 2, 3])
py> y in [1, y]
------------------------------------------------------------
Traceback (most recent call last):
File "<ipython console>", line 1, in <module>
<type 'exceptions.ValueError'>: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
py> y is [1, y][1]
True

I think it skips straight to __eq__ if the element is not the first in the list. That no one acknowledges this makes me feel like a conspiracy is afoot.
.

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