[Numpy-discussion] comparing string array with None raises ValueError, more opinions please

Todd Miller jmiller at stsci.edu
Thu Jun 24 12:15:02 CDT 2004


On Thu, 2004-06-24 at 14:53, Rick White wrote:
> On 24 Jun 2004, Todd Miller wrote:
> 
> > OK,  I see your point.  I talked it over with Perry and he made a
> > reasonable case for allowing comparisons with None (or any object).
> > Perry argued that since None is a common default parameter value, it
> > might simplify code to not have to add logic to handle that case.
> >
> > If no one objects,  I'll change numarray.strings so that comparison of a
> > string array with any object not convertible to a string array results
> > in an array of False values.
> >
> > Any objections?
> 
> Hmm, before you do that you might look at this:
> 
>     >>> import numarray
>     >>> b = numarray.zeros(10)
>     >>> b==0
>     array([1, 1, 1, 1, 1, 1, 1, 1, 1, 1], type=Bool)
>     >>> b==None
>     0
> 
> So comparing numeric arrays to None returns a scalar false value since
> the variable b is not None.

Oh yeah...  I forgot about that.  Numeric comparisons have a special
case for None and blow up for most other arbitrary objects.  So there's
also:

>>> a= numarray.arange(100)
>>> a == None
0
>>> class foo:
..     pass
..
>>> a == foo
Traceback (most recent call last):
..
TypeError: UFunc arguments must be numarray, scalars or numeric
sequences

> I figure that the behavior of comparisons to None for string arrays
and
> numeric arrays ought to be consistent.  I don't know which is
> preferred...

So the two choices now on the table are:

1. Change string equality comparisons to return an array of false or
true for objects which don't convert to strings.  Change Numeric
equality comparisons in a similar fashion.

2. Special case string equality comparisons for None, as is done with
numerical comparisons.  Raise a type error for objects (other than None)
which don't convert to string arrays.

I think I like 2.  Other opinions on 1 & 2?  Other choices?

Regards,
Todd







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