I'm not mistaking it at all. Yes, duck typing is very much liberal acceptance, but Python code tends to go much farther. I could give a million examples -- like how in Python's isinstance() the second argument can be a type or a tuple of types, or in sqlite3 that you can run queries on a connection or on a cursor, and don't even get me started on Matplotlib or Numpy. It's just idiomatic in Python to make things easy for the programmer by accepting multiple types when possible. If you don't recognize this as the common Python pattern, I literally don't know what else to tell you.