[Python-Dev] Fuzziness in io module specs

MRAB python at mrabarnett.plus.com
Fri Sep 18 22:24:52 CEST 2009

James Y Knight wrote:
> 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().
"making things up"? I'm just expressing an opinion!

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