List manipulation

Add multiple items to an existing list in a single operation.

Data processing: concatenating a list with another sequence; Web scraping: accumulating URLs into a list

Common in Python scripts, data‑processing pipelines, and any code that builds collections dynamically.

list.extend(iterable)

list.extend(...)

iterable: any iterable (list, tuple, generator, etc.)

• list
• extend
• iterable
• for loop
• += operator (though not equivalent)

• my_list += iterable
• my_list = my_list + list(iterable)
• for x in iterable: my_list.append(x)

Passing a non‑iterable (e.g., a single int) causing TypeError; expecting extend to add the iterable as a single nested element rather than its items.

list.append adds the whole object as one element, while list.extend adds each element of the iterable individually.

Coming from JavaScript's array.push, which can take multiple arguments; in Python push is append, not extend.

• list.append
• list.insert
• list.remove
• list.pop

extend works in‑place and consumes generators; using the same list as the source can produce unexpected results.

Using extend efficiently adds multiple items to a list in-place, avoiding unnecessary copies and improving performance.

Think of a conveyor belt that adds boxes to the end of a line without stopping the belt.

Note: extend returns None, so avoid using it in expressions where a list is expected (e.g., do not assign the result to a variable).

Consider using itertools.chain for combining multiple iterables without building intermediate lists.