[Numpy-discussion] Multiplying numpy floats and python lists

Tony S Yu tsyu80@gmail....
Sun Jun 20 16:13:00 CDT 2010


On Jun 20, 2010, at 2:28 PM, Pauli Virtanen wrote:

> su, 2010-06-20 kello 13:56 -0400, Tony S Yu kirjoitti:
>> I came across some strange behavior when multiplying numpy floats and
>> python lists: the list is returned unchanged:
>> 
>>> In [18]: np.float64(1.2) * [1, 2]
>>> 
>>> Out[18]: [1, 2]
> 
> Probably a bug, it seems to round the result first to an integer, and
> then do the usual Python thing (try for example np.float64(2.2)).
> 
> I'd suggest filing a bug ticket.

Done: http://projects.scipy.org/numpy/ticket/1516

> 
> Looking at CPython source code, the issue seems to be that np.float64
> for some reason passes PyIndex_Check.
> 
> But (without whipping out gdb) I can't understand how this can be: the
> float64 scalar type is not supposed to have a non-NULL in the nb_index
> slot. Indeed, a np.float64.__index__ method does not exist, and the
> following indeed does not work:
> 
> 	[1, 2, 3][np.float64(2.2)]
> 
> Strange.
> 
> -- 
> Pauli Virtanen
> 
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