Loop in Python: Do stuff before first iteration

Question

I want to optimize.

Simple solution

connection = get_db_connection()
for item in my_iterator:
    push_item_to_db(item, connection)

Drawback:

get_db_connection() is slow. If my_iterator is empty, then I want to avoid to call it.

"if None" solution

connection = None
for item in my_iterator:
    if connection is None:
        connection = get_db_connection()
    push_item_to_db(item, connection)

Drawback:

If there are 100k items in my_iterator, then if connection is None gets called 100k times (although it is needed only once). I want to avoid this.

Perfect solution ...

1. don't call get_db_connection() if iterator is empty
2. don't call if connection is None: uselessly for every iteration.

Any idea?

Answer 1

You can do something like:

connection = None
for item in my_iterator:
    if connection is None:
        connection = get_db_connection()
    push_item_to_db(item, connection)

Simple solution. Don't need to overthink it. Even with 100k operations, x is None is just a reference comparison taking one Python opcode. You really don't need to optimise this compared to a full tcp roundtrip + disk write that happens on every insert.