[Numpy-discussion] Problems casting object arrays to string type on Ubuntu

Dan Yamins dyamins@gmail....
Tue Nov 24 13:46:43 CST 2009


> I suspect you're running into this bug:
>
> http://projects.scipy.org/numpy/ticket/1235
>
> This has been fixed in SVN r7514, (and thus 1.4 pre releases), so it's
> not a platform difference.
>

Great, thanks for the reply!

best,
Dan



> > <mailto:dyamins@gmail.com>> wrote:
> >
> >     Hi all,
> >
> >     I'm having some issues casting object arrays to string type,
> >     especially on my Ubuntu installation. (Ubuntu Jaunty, 9.04, with
> >     Numpy v. 1.3.)
> >
> >     With small arrays, the conversion is just wrong.  With large
> >     arrays, there seems to be some memory corruption.   Conversion to
> >     int or float (when appropriate) seems to work.
> >
> >     For instance, here are some examples of errors with small arrays:
> >
> >       >>> X = numpy.array([13,14],'object')
> >       >>> X.astype('|S2')
> >       array(['13', '\xb2'],
> >           dtype='|S2')
> >       >>> X.astype('int')      #conversion to int or float seems to
> >     work fine
> >       array([13, 14])
> >       >>> X.astype(float)
> >       array([ 13.,  14.])
> >       >>> X = numpy.array(['cat','bat'],'object')
> >       >>> X.astype('|S3')
> >       array(['cat', '\x00ba'],
> >            dtype='|S3')
> >
> >     Large arrays:
> >
> >        In [24]: X = numpy.array(['cat','bat']*300000,'object')
> >        In [25]: Y = X.astype('|S3')
> >        *** glibc detected *** /usr/bin/python: munmap_chunk(): invalid
> >     pointer: 0xb7cd5008 ***
> >
> >
> >     I do NOT have this problem with Numpy 1.4.0.dev7746, installed on
> >     my OSX 10.5.8 machine.   There, everything seems to work fine.
> >
> >     What's going on?  I feel like I've seem some traffic about related
> >     issues on the list before, but I couldn't quite tell from reading
> >     the threads what the "final upshot" of the discussion was ...
> >     Is this something that was fixed in recent NumPy 1.4 releases, or
> >     is something about my Ubuntu vs. OSX installations?    Generally
> >     speaking can I / should I be relying on casting from object arrays
> >     to do the "right" (or "intuitive") thing?
> >
> >     thanks,
> >     Dan
> >
> >
> > ------------------------------------------------------------------------
> >
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> >
>
> --
> Michael Droettboom
> Science Software Branch
> Operations and Engineering Division
> Space Telescope Science Institute
> Operated by AURA for NASA
>
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