How do I determine the proper `paramstyle` when all I have is a `Connection` object?

Question

I have an instance of a Connection (required to DB API 2.0-compliant), but I don't have the module from which it was imported. The problem is that I am trying to use named parameters, but I don't know which paramstyle to use.

Since paramstyle is a module-level constant, I can't just ask the Connection. I tried using inspect.getmodule() on my Connection instance, but it just returned None. Is there an easier way that I'm just missing, or will I need to do some try/except code to determine which paramstyle to use?

Thanks.

Answer 1

Where did you get the instance from? I can't imagine a situation where you won't know the beforehand the source of the connection. If the user of your library is passing you a connection, ask him for the paramstyle as well.

Anyway, look at the following console session:

>>> import sqlite3
>>> c = sqlite3.connect('/tmp/test.db')
>>> c
<sqlite3.Connection object at 0xb7db2320>
>>> type(c)
<type 'sqlite3.Connection'>
>>> type(c).__module__
'sqlite3'
>>> import sys
>>> sys.modules[type(c).__module__].paramstyle
'qmark'

However that sucks. I wouldn't rely on it not even for a second. I use my own connection-like objects, and I'd like to pass one of those to your library. I'd hate it when it tries to magically find out the paramstyle and fails because I am using a connection-like wrapper object.

Answer 2

Pass type(connection) (connection class) to inspect.getmodule(), not connection object. The class tracks the module it was defined in so inspect can find it, while object creation is not tracked.

Answer 3

You can't.

You can try by looking at connection.__class__.__module__, but it's not specified by DB-API that it'll work. In fact for many common cases it won't. (eg. the class is defined in a submodule of the package that acts as the DB-API module object; or the class is a C extension with no __module__.)

It is unfortunate, but you will have to pass a reference to the DB-API module object around with the DB-API connection object.