Python sqlite3 placeholder

问题:

is there a way to set the placeholder for queries in sqlite3 ? I have some functions that work with a database and it would be more satisfying if they could work both with mysql and sqlite. Mysql and Postgres python apis use the %s as a placeholder, but sqlite3 use a question mark instead.

I'm looking for a way to use the same placeholder whatever the database engine.

Thanks for your help.

回答1:

Updated to fix my earlier error about how to use the paramstyle global

If the DB modules you use follow the Python Database API Specification v2.0, you can get the module global paramstyle which should be any of these:

1. 'qmark' Question mark style, e.g. '...WHERE name=?'
2. 'numeric' Numeric, positional style, e.g. '...WHERE name=:1'
3. 'named' Named style, e.g. '...WHERE name=:name'
4. 'format' ANSI C printf format codes, e.g. '...WHERE name=%s'
5. 'pyformat' Python extended format codes, e.g. '...WHERE name=%(name)s'

You can then compose your SQL statements with the placeholder used by the module. You can do something like this:

import sqlite3

paramstyle = sqlite3.paramstyle

if paramstyle == 'qmark':
    ph = "?"
elif paramstyle == 'format':
    ph = "%s"
else:
    raise Exception("Unexpected paramstyle: %s" % paramstyle)

sql = "INSERT INTO foo VALUES (%(ph)s, %(ph)s, %(ph)s)" % { "ph" : ph }

回答2:

The underlying library doesn't support %s, so it would need to be replaced manually. It might be easier to check the paramstyle attribute and replace all instances of a different placeholder in the query with an appropriate value instead.