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To: python-list@python.org
From: Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject: Re: Try-except for flow control in reading Sqlite
Date: Mon, 28 Oct 2013 19:43:19 -0400
Organization: IISS Elusive Unicorn
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On Sun, 27 Oct 2013 20:43:07 -0700 (PDT), Victor Hooi
<victorhooi@gmail.com> declaimed the following:

>Hi,
>
>I'd like to double-check something regarding using try-except for controlling flow.
>
>I have a script that needs to lookup things in a SQLite database.
>
>If the SQLite database file doesn't exist, I'd like to create an empty database, and then setup the schema.
>
>Is it acceptable to use try-except in order to achieve this? E.g.:
>
>    try:
>        # Try to open up the SQLite file, and lookup the required entries
>    except OSError:
>        # Open an empty SQLite file, and create the schema
>
>
	In my experience, SQLite will /create/ an empty database file if the
specified name does not exit. So just executing the connect() call is all
that is needed. After all, checking for data IN the database will either
return something or fail at that point in which case you can now populate
the schema.

-=-=-=-=-=-
>>> import sqlite3 as db
>>> con = db.connect("anUnknown.db")
>>> cur = con.cursor()
>>> rst = cur.execute("pragma table_info('aTable')")
>>> rst
<sqlite3.Cursor object at 0x0000000004725C00>
>>> for ln in rst:
... 	print ln
... 	
>>> for ln in cur:
... 	print ln
... 	
>>> rst = cur.execute("create table aTable ( junk varchar )")
>>> con.commit()
>>> rst = cur.execute("pragma table_info('aTable')")
>>> for ln in rst:
... 	print ln
... 
(0, u'junk', u'varchar', 0, None, 0)
>>> 


	No try/except needed -- just an a conditional testing the length of the
result returned by the pragma instruction on the table you expect to find
in the database.
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/