[Numpy-discussion] Re ading scientific notation using D instead of E

Christopher Barker Chris.Barker@noaa....
Fri Feb 12 15:51:57 CST 2010


Robert Kern wrote:
> Eh, what? numpy.float is Python's float. No numpy features at all.

my mistake -- I guess I assumed that numpy.float was an alias for 
numpy.float64.

anyway, the (all?) the numpy dtypes have their own implementation of 
conversion from strings (which are a bit buggy, unfortunately).

They don't seem to be accessible in the same way, though:

In [44]: np.float64('1.23F+04')
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)

/Users/cbarker/HAZMAT/SmallTools/WxTool/trunk/tests/<ipython console> in 
<module>()

ValueError: setting an array element with a sequence.

is the only way to do this:

In [49]: np.fromstring('1.23', dtype=np.float64, sep=' ')
Out[49]: array([ 1.23])

which is indeed, buggy (I wasn't aware of this bug yet):

In [51]: np.fromstring('1.23F+04', dtype=np.float64, sep=',')
Out[51]: array([ 1.23])

This make me think that the string conversion code is only being used by 
fromstring/fromfile, and that it isn't used much there!

Which makes me wonder -- should we fix it or deprecate it?

If fix_it:

I wonder about the choice of strtod() and friends for the string 
conversion -- is seems that fscans would be easier and more robust (or 
easier to make robust, anyway)

-Chris





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Christopher Barker, Ph.D.
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