[issue34446] ambiguous _max_size parameter in SpooledTemporaryFile

[Andrew Scheller]

Andrew Scheller  added the comment:

I agree that this is ambiguous behaviour. The docs at 
https://docs.python.org/3/library/tempfile.html#tempfile.SpooledTemporaryFile 
say "This function operates exactly as TemporaryFile() does, except that data 
is spooled in memory until the file size exceeds max_size, or until the file’s 
fileno() method is called, at which point the contents are written to disk and 
operation proceeds as with TemporaryFile().", and as the default value for 
max_size is 0, that would imply to me that _any_ data written to a 
SpooledTemporaryFile (constructed with a max_size of 0) would instantly get 
(internally) converted to a TemporaryFile.

Whereas looking at the code 
https://github.com/python/cpython/blob/master/Lib/tempfile.py#L650 it seems a 
max_size of 0 means "don't rollover". Perhaps it would have made sense to have 
SpooledTemporaryFile default to a max_size of None (and use that to mean "never 
rollover") ?

So as well as the inconsistency between rollover behaviour in the 
write()/writelines() methods and the truncate() method (when max_size is 0) 
that jcc2220 pointed out, I believe there's also a documentation issue here in 
that it's not clear what a max_size of 0 is /supposed/ to do.

--
assignee:  -> docs@python
components: +Documentation
nosy: +docs@python, lurchman
versions: +Python 2.7, Python 3.5, Python 3.6, Python 3.8, Python 3.9

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue34446] ambiguous _max_size parameter in SpooledTemporaryFile

[jcc2220]

jcc2220  added the comment:

Here's an example of the inconsistency - if SpooledTemporaryFile is 
instantiated with max_size set to 0, it will not rollover, EXCEPT when truncate 
method is called.  Both write and writelines (public methods) call _check, 
which deals with rollover, but _check will never rollover if max_size is set to 
0.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue34446] ambiguous _max_size parameter in SpooledTemporaryFile

[Brett Cannon]

Brett Cannon  added the comment:

Do realize that anything which starts with an underscore, like _check, is 
considered a private API.

--
nosy: +brett.cannon

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue34446] ambiguous _max_size parameter in SpooledTemporaryFile

[jcc2220]

New submission from jcc2220 :

When _max_size is set to 0, the _check method will never call rollover, as the 
conditional for a rollover is never satisfied.  However, in the truncate 
method, the _max_size is not checked against 0, and so a rollover could be 
called when it is 0.  This is more of an issue of consistency - should 0 mean 
that it will never rollover?  If so, truncate should be modified.  Should 0 be 
interpreted as 'always rollover'?  If so, the _check should be modified.  
Personally, I'd rather have something like -1 mean never, 0 mean always, and >0 
mean only when greater than specified size.


John

--
components: Library (Lib)
messages: 323809
nosy: jcc2220
priority: normal
severity: normal
status: open
title: ambiguous _max_size parameter in SpooledTemporaryFile
type: behavior
versions: Python 3.7

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com