[Tutor] How to test for the existence of a table in a sqlite3 db?
robertvstepp at gmail.com
Sun Oct 15 01:48:27 EDT 2017
On Sun, Oct 15, 2017 at 12:07 AM, boB Stepp <robertvstepp at gmail.com> wrote:
> #!/usr/bin/env python3
> """This file starts the blood pressure readings program."""
> import sqlite3
> def ensure_db(filename):
> """Open the database, "filename", if it exists; otherwise, create a
> database named "filename"."""
> db = sqlite3.connect(filename)
> cur = db.cursor()
> sql_cmd = "SELECT VersionNumber FROM CurrentDBVersion"
> # First element of returned tuple will be the db version number:
> current_db_version = int(cur.execute(sql_cmd).fetchone())
> except sqlite3.OperationalError:
> # This means that the database and the table, "CurrentDBVersion", has
> # not yet been created, implying "version 0".
> current_db_version = 0
> sql_scripts = ["../database/create_sqlite3_db.sql"]
> for sql_scriptname in sql_scripts[current_db_version:]:
> with open(sql_scriptname) as f:
> return db
I have not used a "finally" block before. I just had the thought that
maybe it would run even if an uncaught exception might occur. I tried
to test this thought by generating a deliberate NameError in the "try"
block and added a print to the "finally" clause. I got the intended
NameError with no evidence of the added print printing. But I thought
I would ask just to be sure: If an uncaught exception occurs, will
the "finally" clause execute?
> I have chickened out and not done a TDD approach yet. I will probably
> pause here, wait for feedback from this list, and try to figure out
> how I should test what I have so far. And how do you test SQL scripts
> Some things I am still pondering:
I forgot to add (5):
5) How should I handle the cursor object? When I should I close it?
My function returns "db" which I presume keeps the connection to the
database. But what happens to the cursor object as I have written the
function, since I never closed it?
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