Thanks for everyone's help and thoughts.  I agree that this behavior is 
buggy.  I submitted a bug report to the python project at sourceforge, 
with a link to this thread.  Hopefully the report will be helpful.

tim

Charles R Harris wrote:
> 
> 
>  On 12/12/06, *Travis Oliphant* <oliphant@[...].edu 
>  <mailto:oliphant@[...].edu>> wrote:
> 
>      Tim Hirzel wrote:
> 
>      >Good thought Chris,
>      >Normal reading and writing does seem to work. ..
>      >But, my friend Daniel figured out a workaround when I asked to
>      confirm
>      >this behavior on his windows setup (and it is does behave the
>      same for
>      >him).  The first clue was this:
>      >
>      > >>> f = tempfile.TemporaryFile()
>      > >>> type(f)
>      ><type 'instance'>
>      > >>> g = open("temp","w+b")
>      > >>> type(g)
>      ><type 'file'>
>      >
>      >so Daniel did a dir(f) and found the 'file' attribute
>      >
>      >so if you do (where 'a' is a numpy array)
>      > >>> a.tofile(f.file)
>      >It works!
>      >
>      >writing to the "file" attribute of the TemporaryFile, it works
>      fine!  So
>      >that's good, but still a little hinky.  Especially since it works on
>      >linux...
>      >on a linux platform, what does type( tempfile.TemporaryFile())
>      return?  I
>      >assume an <type 'instance'>  as well...
>      >
>      >anways, so at least there is a quick repair for now.  Good news is, I
>      >assume using 'f.file' would work on linux too in terms of having a
>      >single cross-platform solution.
>      >
>      >
>      There is no file attribute on Linux.   On linux you get
> 
>      >>> type(f)
>      <type 'file'>
> 
>      So, you might have to do something like:
> 
>      if not isinstance(f, file):
>         f = f.file
> 
>      before passing f to the tofile method.
> 
>      It seems to me that the temporary file mechanism on Windows is a
>      little
>      odd.
> 
> 
>  Looks like a tempfile bug to me. Python should be cross platform and 
>  since the file attribute is correctly set on windows, I don't see why 
>  the tempfile can't be made to behave correctly.
> 
>  Chuck
> 
> 
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