Steven D'Aprano wrote:
On Sun, 07 Dec 2008 13:57:54 -0800, James Stroud wrote:
Rasmus Fogh wrote:
ll1 = [y,1]
y in ll1
True
ll2 = [1,y]
y in ll2
Traceback (most recent call last):
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()
I think you could be safe calling this a bug with numpy.
Only in the sense that there are special cases where the array elements
are all true, or all false, and numpy *could* safely return a bool. But
special cases are not special enough to break the rules. Better for the
numpy caller to write this:
a.all() # or any()
instead of:
try:
bool(a)
except ValueError:
a.all()
as they would need to do if numpy sometimes returned a bool and sometimes
raised an exception.
I'm missing how a.all() solves the problem Rasmus describes, namely that
the order of a python *list* affects the results of containment tests by
numpy.array. E.g. "y in ll1" and "y in ll2" evaluate to different
results in his example. It still seems like a bug in numpy to me, even
if too much other stuff is broken if you fix it (in which case it
apparently becomes an "issue").
James
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