Rich Comparisons Gotcha

James Stroud jstroud at
Mon Dec 8 09:10:20 CET 2008

Robert Kern wrote:
> James Stroud wrote:
>> I think it skips straight to __eq__ if the element is not the first in 
>> the list.
> No, it doesn't skip straight to __eq__(). "y is 1" returns False, so 
> (y==1) is checked. When y is a numpy array, this returns an array of 
> bools. list.__contains__() tries to convert this array to a bool and 
> ndarray.__nonzero__() raises the exception.
> list.__contains__() checks "is" then __eq__() for each element before 
> moving on to the next element. It does not try "is" for all elements, 
> then try __eq__() for all elements.

Ok. Thanks for the explanation.

>  > That no one acknowledges this makes me feel like a conspiracy
>  > is afoot.
> I don't know what you think I'm not acknowledging.

Sorry. That was a failed attempt at humor.


More information about the Python-list mailing list