constructor:
    config(Dict): Database connection params
    db_type(str): Database type
usage:
    from slim_helper.db_helper import DbHelper
    # SQlite:
    config = {'dbname': ':memory:'}
    with DbHelper(config, 'sqlite') as db:
        db.execute("""
             CREATE TABLE foo (
             id INTEGER PRIMARY KEY ,
             txt TEXT
             )
             """)
        db.execute("insert into foo values(?,?)", [1, 'a'])
        db.execute("insert into foo values(?,?)", [2, 'b'])
        db.execute("insert into foo values(?,?)", [3, 'c'])
        db.commit()
        result,columns = db.query("select * from foo where id=? and txt=?", [2, 'b'])
        print(result,columns)
    # Or
    db = DbHelper(config, 'sqlite')
    db.open()
    ...
    db.close()


    # PostgreSQL:
    config = {'host': 'localhost', 'port': '5432',
              'dbname': 'foobar', 'user': 'foobar', 'password': 'foobar'}
    with DbHelper(config, 'postgresql') as db:
        db.execute("""
            CREATE TABLE foo (
            id INTEGER PRIMARY KEY ,
            txt TEXT
            )
            """)
        db.execute("insert into foo values(%s,%s)", [1, 'a'])
        db.execute("insert into foo values(%s,%s)", [2, 'b'])
        db.execute("insert into foo values(%s,%s)", [3, 'c'])
        db.commit()
        result,columns = db.query("select * from foo where id=%s and txt=%s", [2, 'b'])
        print(result,columns)
    # Or
    db = DbHelper(config, 'postgresql')
    db.open()
    ...
    db.close()


    # Oracle:
    config = {'host': 'localhost', 'port': '1521', 'dbname': 'foobar',
              'user': 'foobar', 'password': 'foobar', 'mode': None}
    with DbHelper(config, 'postgresql') as db:
        db.execute("""
            CREATE TABLE foo (
            id INTEGER PRIMARY KEY ,
            txt VARCHAR2(100)
            )
            """)
        db.execute("insert into foo values(:1,:2)", [1, 'a'])
        db.execute("insert into foo values(:1,:2)", [2, 'b'])
        db.execute("insert into foo values(:1,:2)", [3, 'c'])
        db.commit()
        result,columns = db.query("select * from foo where id=:1 and txt=:2", [2, 'b'])
        print(result,columns)
    # Or
    db = DbHelper(config, 'oracle')
    db.open()
    ...
    db.close()

multiprocessing.Pool helper
constructor:
    task (Task): Task object.
    arguments (Iterable[Iterable]):arguments list.
    parallel (int): parallel
usage:
    from slim_helper.parallel_helper import Pool, Task
    def test(a: int, b: str):
        print(a, b)
        return str(a)+b
    p1 = (1, 'a')
    p2 = (2, 'b')
    p3 = (3, 'c')
    task = Task(test)
    params = (p1, p2, p3, p1, p2, p3)
    pool = Pool(task, params, 2)
    r = pool.start()
    print(r)