What is a function in Python?

A function in Python is defined as a block of reusable code designed to perform a single action or task. This means that when you create a function, you're able to encapsulate a specific set of operations that can be executed whenever the function is called. This promotes the principle of code reuse, which makes it easier to maintain and organize code by reducing redundancy. Functions can accept parameters and may return values, shaping their behavior and output based on the input provided.

The other options describe different concepts. A data type refers to the classification of data (like integers, strings, lists) but does not encompass the functionality of code execution. The method for iterating over a collection refers to techniques such as loops (e.g., for or while) that process items one at a time, rather than defining a reusable block of instructions. An error-handling mechanism typically pertains to techniques like try-except blocks that allow a program to manage exceptions and errors, which is unrelated to the definition of a function itself.