This page follows the examples from the official documentation on expressions in python

and

PEP 572

Some expressions

Assignement expressions

ORDERS = [{"id": "one"}, {"id": "two"}] 
order_id = "one"
if order := [order for order in ORDERS if order['id'] == order_id]:
    print(f"Order id {order_id} found!")

The above code is equivalent to checking the property of the list (len) to see if it is empty or not

order_id = 'one'
order = [order for order in ORDERS if order['id']==order_id]
if len(order) > 0:
    print(f"Order id {order_id} found!")