In article
<2eeb1c54-83f5-4375-93fb-478bdbd7e...@j25g2000yqa.googlegroups.com>,
Jon Clements <jon...@googlemail.com> wrote:
> On 12 Oct, 18:32, Roy Smith <r...@panix.com> wrote:
> > On Oct 12, 1:20 pm, Jon Clements <jon...@googlemail.com> wrote:
> >
> > > On 12 Oct, 16:10, Roy Smith <r...@panix.com> wrote:
> >
> > > > PEP 249 says about executemany():
> >
> > > > Prepare a database operation (query or command) and then
> > > > execute it against all parameter sequences or mappings
> > > > found in the sequence seq_of_parameters.
> >
> > > > are there any plans to update the api to allow an iterable instead of
> > > > a sequence?
> >
> > > I'm not understanding (probably me). Example?
> >
> > I have a dictionary, d, which has a million items in it, and want to
> > do something like:
> >
> > executemany("update foo set bar = %s where id = %s",
> > d.iteritems())
> >
> > If executemany accepted an iterable, that would work. But, it only
> > accepts a sequence, so I need to do:
> >
> > executemany("update foo set bar = %s where id = %s", d.items())
> >
> > which generates a million-item temporary list. Or am I mis-
> > understanding the PEP?
>
> Interesting, but here's my guess...
>
> Replace d.items() with itertools.repeat( ('a', 'b') )
>
> So, if you have a sequence, which has a length and known size, at
> least you can have an attempt at the DB operations: whether the
> transaction fails or not is another thing...In short, a sequence is
> finite, while an iterable may be infinite.
Also, keep in mind that PEP 249 DB adapter implementations are typically
wrappers around a lower-level client library for a particular DB
implementation and that most of those client APIs - written in C - will
likely require all of the items to be passed in one call. If so, the DB
adapter would need to immediately evaluate the iterable and produce a
list in memory anyway.
--
Ned Deily,
n...@acm.org
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