[Numpy-discussion] TypeError in dtype.__eq__()

Bryan Cole bryan@cole.uklinux....
Sun Jan 11 15:13:24 CST 2009


> > However, also note
> > that with ndarray's rich comparisons, such membership testing will
> > fail with ndarrays, too.
> 
> This poses a similarly big problem. I can't understand this behaviour
> either:

OK, I can now. After equality testing each item, the result must be cast
to bool. This is where the truth-testing comes in.

Testing array membership in lists does work, just so long as there are
no numerical objects in the list. Any/only equality comparisons which
return another (bool) ndarray will cause the exception. Thus, the error
is not triggered in PyYAML.

FWIW, I don't like the policy of forbidding truth testing on bare
arrays. I'd prefer that ndarray.__nonzero__() implicitly call
ndarray.all(). For my use-cases, this is what I want >90% of the time.
Where any() is required, this must be made explicit. However, I
understand the logic behind raising an exception and presumably others
prefer this.

Ultimately, I'm forced to conclude that the idea that membership testing
should always succeed was bogus. Bummer.

BC




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