Python: How to successfully inherit Sqlite3.Cursor and add my customized method

Question

I want to make my own MagicCursor class. I want it to inherit all method and attributes from sqlite3.Cursor(). But it looks not that easy in t his case.

usually we create a cursor like this:

import sqlite3
conn = sqlite3.connect('test.db')
crs = conn.cursor()

because there's a connection in between. So I think I have to define my own Connection Class and then define my own Cursor.

Here's what I want to implement:

import sqlite3
conn = MyConnect('test.db') ## this returns me a connect object, inherit from         sqlite3.Connection 
crs = conn.cursor() ## this returns me a MyCursor class,
                ## which inherit from sqlite3.Cursor() and has my customized method

Here's my code, but failed.

class MyConnect(sqlite3.Connection):
    def cursor(self):
        return MyCursor(self)

class MyCursor(sqlite3.cursor):
    def __init__(self, connect):
        self = connect.cursor()

    def mymethod1(self, argv)
         ...... return ...... ## what ever I defined

Anyone got an idea how to implement that?

I do not believe you want to reassign self like you do in your __init__ method. Shouldn't that be sqlite3.cursor.__init__(self) (or something close)? Sqlite3 is a compiled extension on my system - you'd have to look up the call signature and see how (or if) it supports a connection parameter. You may not be able to go about adding a method to a compiled extension in this way. — g.d.d.c
– g.d.d.c, Commented May 15, 2014 at 16:41

unutbu · Accepted Answer · 2014-05-15 16:53:24Z

6

import sqlite3
class MyConnect(sqlite3.Connection):
    def cursor(self):
        return super(MyConnect, self).cursor(MyCursor)

class MyCursor(sqlite3.Cursor):
    def mymethod1(self, argv):
        print('Got here')

conn = sqlite3.connect(':memory:', factory=MyConnect)
print(conn)
# <__main__.MyConnect object at 0x90db66c>

cursor = conn.cursor()
print(cursor)
# <__main__.MyCursor object at 0x90d19dc>

cursor.mymethod1('foo')
# Got here

In this example, super(MyConnect, self).cursor(MyCursor) calls sqlite3.Connection.cursor(MyCursor).

sqlite3.Connection.cursor accepts an optional argument, cursorClass. When supplied, that is the class used to instantiate the cursor.

edited May 15, 2014 at 16:53

answered May 15, 2014 at 16:47

unutbu

886k197 gold badges1.9k silver badges1.7k bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

MacSanhe Over a year ago

It works!! Thank you!! Could you tell me how could this works?

unutbu Over a year ago

super calls the cursor method of (roughly speaking) a parent class of MyConnect. In this case, sqlite3.Connection.cursor.

unutbu Over a year ago

More accurately, super(MyConnect, self).cursor() calls the cursor method of the next class in MyConnect's MRO after type(self). That may or may not be a parent class of MyConnect.

Collectives™ on Stack Overflow

Python: How to successfully inherit Sqlite3.Cursor and add my customized method

1 Answer 1

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related