[Numpy-discussion] annoying numpy string to float conversion behaviour

[David M. Cooke]

On Jun 20, 2007, at 04:35 , Torgil Svensson wrote:

> Hi
>
> Is there a reason for numpy.float not to convert it's own string
> representation correctly?

numpy.float is the Python float type, so there's nothing we can do. I  
am working on adding NaN and Inf support for numpy dtypes, though, so  
that, for instance, numpy.float64('-1.#IND') would work as expected.  
I'll put it higher on my priority list :-)

> Python 2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC v.1310 32 bit
> (Intel)] on win32>>> import numpy
>>>> numpy.__version__
> '1.0.3'
>>>> numpy.float("1.0")
> 1.0
>>>> numpy.nan
> -1.#IND
>>>> numpy.float("-1.#IND")
> Traceback (most recent call last):
>  File "<pyshell#20>", line 1, in <module>
>    numpy.float("-1.#IND")
> ValueError: invalid literal for float(): -1.#IND
>>>>
>
> Also, nan and -nan are represented differently for different float to
> string conversion methods. I guess the added zeros are a bug
> somewhere.
>>>> str(nan)
> '-1.#IND'
>>>> "%f" % nan
> '-1.#IND00'
>>>> str(-nan)
> '1.#QNAN'
>>>> "%f" % -nan
> '1.#QNAN0'
>
> This is a problem when floats are stored in text-files that are later
> read to be numerically processed. For now I use the following to
> convert the number.
>
> special_numbers=dict([('-1.#INF',-inf),('1.#INF',inf),
>                       ('-1.#IND',nan),('-1.#IND00',nan),
>                       ('1.#QNAN',-nan),('1.#QNAN0',-nan)])
> def string_to_number(x):
>    if x in special_numbers:
>        return special_numbers[x]
>    return float(x) if ("." in x) or ("e" in x) else int(x)
>
> Is there a simpler way that I missed?
>
> Best Regards,
>
> //Torgil
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>

-- 
|>|\/|<
/------------------------------------------------------------------\
|David M. Cooke              http://arbutus.physics.mcmaster.ca/dmc/
|cookedm at physics.mcmaster.ca

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