How to check if a SQLite3 database exists in Python?

I am trying to create a function in Python 2.7.3 to open a SQLite database.

This is my code at the moment:

import sqlite3 as lite
import sys

db = r'someDb.sqlite'

def opendb(db):
    try:
        conn = lite.connect(db)
    except sqlite3.Error:
        print "Error open db.\n"
        return False
    cur = conn.cursor()
    return [conn, cur]

I have tried the code above and I have observed that the sqlite3 library opens the database declared if exists, or creates a new database if this one doesn't exist.

Is there a way to check if the database exists with sqlite3 methods or I have to use file operation like os.path.isfile(path)?