Re: [Numpy-discussion] Scalars, comparisons and indexing. Is this a bug?

[Bill Baxter]

I believe that's the problem that the indexing PEP from Travis is
supposed to address:
  http://www.python.org/dev/peps/pep-0357/
So I think there's not much anyone can do about it untill the PEP is
accepted and implemented.

Maybe you can cast to int?
 In [34]: (1,2)[int(a[0]==b)]


--bb

On 7/15/06, Fernando Perez [EMAIL PROTECTED] wrote:
 Hi all,

 I just got bit by this problem, and I'm not really sure if this is
 something that should be considered a numpy bug or not.  It is a bit
 unpleasant, at the least, though it can be easily worked around.
 Here's a simple demonstration:

 In [32]: a=array([1,2])

 In [33]: b=1

 In [34]: (1,2)[a[0]==b]
 ---
 exceptions.TypeError Traceback (most
 recent call last)

 /home/fperez/research/code/mwmerge/mwadap-merge/mwadap/test/ipython console

 TypeError: tuple indices must be integers


 Whereas this works:

 In [35]: c=2

 In [36]: (1,2)[c==b]
 Out[36]: 1

 Basically, it seems that array scalars, upon comparisons, return
 something that doesn't 'looke enough like an int' to python for it to
 let you use it as an index, it's a 'boolscalar':

 In [38]: a0==b0
 Out[38]: True

 In [39]: type _
 --- type(_)
 Out[39]: type 'boolscalar'


 Advice? Is this a numpy bug?  Or should it just be left alone, and
 this kind of inconvenience will disappear when 2.5 is out, with
 __index__ support?

 Cheers,

 f


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Re: [Numpy-discussion] Scalars, comparisons and indexing. Is this a bug?

[Fernando Perez]

On 7/14/06, Bill Baxter [EMAIL PROTECTED] wrote:
 I believe that's the problem that the indexing PEP from Travis is
 supposed to address:
   http://www.python.org/dev/peps/pep-0357/
 So I think there's not much anyone can do about it untill the PEP is
 accepted and implemented.

 Maybe you can cast to int?
  In [34]: (1,2)[int(a[0]==b)]

Yup, that's the workaround I'm using.

I was just wondering if comparisons between array scalars shouldn't
return /true/ booleans (which can be used as indices) instead of array
scalar booleans.  I realize that the __index__ support in 2.5 will
make this point moot (the PEP you point to), but perhaps this
particular one can actually be fixed today, for all users of python
pre-2.5.  However, I haven't really wrapped my head enough around all
the subtleties of array scalars to know whether 'fixing' this
particular problem will introduce other, worse ones.

Cheers,

f


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