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| References | <e1a94d90-57b4-4f6c-be9a-bef08f978639@h13g2000vbn.googlegroups.com> <CALwzidmkSPAQBUxHTUWdoj+QKTR91UO_EPoMxr+2G+Qcy4PZdw@mail.gmail.com> <CAGeFqcC=hc5xMgwqLAbdMR=cCdjYVhAbQvS9yeaxMH=o766_mA@mail.gmail.com> |
|---|---|
| From | Ian Kelly <ian.g.kelly@gmail.com> |
| Date | 2012-01-09 18:11 -0700 |
| Subject | Re: Explanation about for |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.4567.1326157923.27778.python-list@python.org> (permalink) |
2012/1/9 Νικόλαος Κούρας <nikos.kouras@gmail.com>: > if the MySQL query was: > > cursor.execute( '''SELECT host, hits, agent, date FROM visitors WHERE pin = > %s ORDER BY date DESC''', pin ) > > can you help me imagine how the mysql database cursor that holds the query > results would look like? I must somehow visualize it in order to understand > it! You can think of it as a pointer, traversing over one row of the result set at a time. Hopefully this will come out legibly: ----------------------------------------------- | HOST | HITS | AGENT | DATE | ----------------------------------------------- ------------- | foo | 7 | IE6 | 1/1/11 | <---- | cursor | ----------------------------------------------- ------------- | bar | 42 | Firefox | 2/2/10 | ----------------------------------------------- | baz | 4 | Chrome | 3/3/09 | ------------------------------------------------ > Also what happend if the query was: > cursor.execute( '''SELECT host FROM visitors") ? > > the result would have to be something likelike? > > ----------------- > |somehost1| > ----------------- > |somehost2| > ----------------- > |somehost3| > ----------------- > ..................... > ..................... > |somehost n| > ----------------- > > So what values host, hits, agent, date would have in 'for host, hits, agent, > date in > dataset' ? Every row has one string how can that be split in 4? Why don't you try it and see what happens? But to spare you the suspense, you would get: ValueError: need more than 1 value to unpack Because you can't unpack a 1-length tuple into four variables. The code assumes that the query is selecting exactly 4 columns.
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Explanation about for Νικόλαος Κούρας <nikos.kouras@gmail.com> - 2012-01-09 15:23 -0800
Re: Explanation about for Ian Kelly <ian.g.kelly@gmail.com> - 2012-01-09 16:42 -0700
Re: Explanation about for Chris Rebert <clp2@rebertia.com> - 2012-01-09 15:58 -0800
Re: Explanation about for Ian Kelly <ian.g.kelly@gmail.com> - 2012-01-09 18:11 -0700
Re: Explanation about for Νικόλαος Κούρας <nikos.kouras@gmail.com> - 2012-01-10 01:02 -0800
Re: Explanation about for Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2012-01-10 11:57 +0100
Re: Explanation about for Νικόλαος Κούρας <nikos.kouras@gmail.com> - 2012-01-10 03:38 -0800
Re: Explanation about for Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2012-01-10 14:52 +0200
Re: Explanation about for Νικόλαος Κούρας <nikos.kouras@gmail.com> - 2012-01-10 03:37 -0800
Re: Explanation about for "Frank Millman" <frank@chagford.com> - 2012-01-10 15:39 +0200
Re: Explanation about for Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2012-01-10 16:22 +0100
Re: Explanation about for RainyDay <andrei.avk@gmail.com> - 2012-01-11 14:39 -0800
Re: Explanation about for Nick Dokos <nicholas.dokos@hp.com> - 2012-01-10 10:24 -0500
Re: Explanation about for Νικόλαος Κούρας <nikos.kouras@gmail.com> - 2012-01-11 14:50 -0800
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