Difference between tempfile and spooled tempfile?

[Steve Howell]

On Apr 5, 7:50 am, "Alex van der Spek" <zd... at xs4all.nl> wrote:
> I do not understand why the spooled write gives an error. See below.
> The normal tempfile works just fine. They are supposed to behave equal?
>
> All insight you can provide is welcome.
> Alex van der Spek
>
> +++++++++++++++++++++++++++++++++++++++++++++++++
>
> Python 2.7.1 (r271:86832, Nov 27 2010, 18:30:46) [MSC v.1500 32 bit (Intel)]
> on win32
> Type "copyright", "credits" or "license()" for more information.
>
> >>> import array
> >>> import tempfile
> >>> stf = tempfile.SpooledTemporaryFile(max_size=1024)
> >>> ptf = tempfile.TemporaryFile()
> >>> fff = [float(x) for x in range(2048)]
> >>> ffa = array.array('f',fff)
> >>> ptf.write(ffa)
> >>> stf.write(ffa)
>
> Traceback (most recent call last):
>   File "<pyshell#7>", line 1, in <module>
>     stf.write(ffa)
>   File "C:\Python27\lib\tempfile.py", line 595, in write
>     rv = file.write(s)
> TypeError: must be string or read-only character buffer, not array.array
>

I think the docs are slightly misleading.  While SpooledTemporaryFile
allows you to write(), it's more finicky about serializing arrays,
hence the error message.

If you look under the hood, you'll see that it's mostly a limitation
of StringIO.

http://hg.python.org/cpython/file/2.7/Lib/tempfile.py

   494     """Temporary file wrapper, specialized to switch from
   495     StringIO to a real file when it exceeds a certain size or
   496     when a fileno is needed.
   497     """
   498     _rolled = False
   499
   500     def __init__(self, max_size=0, mode='w+b', bufsize=-1,
   501                  suffix="", prefix=template, dir=None):
   502         self._file = _StringIO()
   503         self._max_size = max_size
   504         self._rolled = False
   505         self._TemporaryFileArgs = (mode, bufsize, suffix,
prefix, dir)

(See line 502.)

   600     def write(self, s):
   601         file = self._file
   602         rv = file.write(s)
   603         self._check(file)
   604         return rv

(See line 602.)

I'm looking at a slightly different version of the module than you,
but hopefully you get the idea.