Extended db cache backend with 'filter() / LIKE' support (and now scheduled cache clean!)

#example
    from django.core.cache import cache
    cache.set('hello_19374', 'some value here') # will set the key hello_19374 to 'some value here'
    cache.set('hello_xfhh', 'some value here') # etc
    cache.set('19374hello', 'some value here') # etc
    cache.set('alal_hello_19374', 'some value here') # etc
    cache.set('lalahellohdgf', 'some value here') # etc
    print cache.filter('hello%') # will show all keys beginning with 'hello'
    print cache.filter('%%') # will show all keys
    print cache.filter('%hello') # will show all keys ending with 'hello'
    print cache.filter('%hello%') # will show all keys containing 'hello'

    cache.clean() # will delete any cache entries which have past their expiry

#app/settings.py
    CACHE_BACKEND = 'app.cache://cache_table_name_goes_here'

#app/cache.py
"Database cache backend."
    from django.core.cache.backends.db import CacheClass as _CacheClass

    from django.core.cache.backends.base import BaseCache
    from django.db import connection, transaction, DatabaseError
    import base64, time
    from datetime import datetime
    try:
        import cPickle as pickle
    except ImportError:
        import pickle

    # Import the threading and time
    import threading

    def RoutineCacheClean():
        # Import the cache
        from django.core.cache import cache

        # Loop forever!
        while True:
            # Clean it!
            try:
                cache.clean()

            except:
                pass

            # Clean every 3 minutes
            time.sleep(60*3)

    def StartCacheClean():
        # Create the new thread
        t = threading.Thread(
            target = RoutineCacheClean
        )

        # Set the thread daemon flag to true
        t.setDaemon(True)

        # Start the thread
        t.start()

    class CacheClass ( _CacheClass ):
        def filter(self, key, default=None):
            lx={}
            cursor = connection.cursor()
            cursor.execute("SELECT cache_key, value, expires FROM %s WHERE cache_key LIKE %%s" % self._table, [key])

            for row in cursor.fetchall():
                if row is not None:
                    now = datetime.now()
                    if row[2] < now:
                        cursor.execute("DELETE FROM %s WHERE cache_key = %%s" % self._table, [row[0]])
                        transaction.commit_unless_managed()
                    else:
                        value = connection.ops.process_clob(row[1])
                        lx[row[0]]=pickle.loads(base64.decodestring(value))

            return lx

        def clean(self):
            cursor = connection.cursor()
            now = datetime.now().replace(microsecond=0)
            cursor.execute("DELETE FROM %s WHERE expires < %%s" % self._table, [str(now)])
            transaction.commit_unless_managed()

    StartCacheClean()