[SciPy-user] "in" vs. looped "=="

Alan G Isaac aisaac@american....
Wed Mar 12 16:16:06 CDT 2008


On Wed, 12 Mar 2008, "R. Padraic Springuel" apparently wrote:
> I have some code that uses a "1. in x" statement early on, 
> where x is a rank-1 ndarray with dtype=float.  This 
> statement returns False and the program continues 
> accordingly.  However, later on in the same code I loop 
> over the elements of x and the statement "x[i] == 1" is 
> evaluated and comes back as True for some elements of x.  
> To my mind, that shouldn't be happening.  Is there 
> a difference in how "1. in x" (i.e.  the __contains__ 
> method of ndarray) and "x[i] == 1." (i.e.  the __eq__ 
> property of float) behave that I'm not aware of? 


There is a difference, if I recall correctly, but it will 
not cause this.

The difference is that ``in`` will first check an item for 
``is`` and then check it for ``__eq__``.

But since this would not affect your results, the most 
likely possibility seems that you are changing the array somehow.

A small example would help.

Cheers,
Alan Isaac





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