[Python-Dev] Fuzziness in io module specs (original) (raw)

James Y Knight foom at fuhm.net
Fri Sep 18 22:08:23 CEST 2009

On Sep 18, 2009, at 3:55 PM, MRAB wrote:

I think that this should be an invariant:

0 <= file pointer <= file size so the file pointer might sometimes have to be moved.

As for the question of whether 'truncate' should be able to lengthen a file, the method name suggests no; if the method name were 'resize', for example, then maybe yes, zeroing the new bytes for security.

Why are you just making things up? There is a vast amount of
precedent for how file operations should work. Python should follow
that precedent and do like POSIX unless there's a compelling reason
not to. Quoting:

    If  fildes  refers  to  a  regular  file,  the ftruncate()

function shall cause the size of the file to be truncated to length. If the size of the file previously exceeded length,
the extra data shall no longer be available to reads on the file. If the file previously was smaller than this size,
ftruncate() shall either increase the size of the file or fail. XSI-conformant systems shall increase the size of the
file. If the file size is increased, the extended area shall appear as if it were zero-filled. The value of the seek
pointer shall not be modified by a call to ftruncate().

James

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