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Python Python Collections (2016, retired 2019) Lists Growing Lists

fahad lashari
fahad lashari
7,693 Points

How is this any different from list.append()?

Just wondering as I had completed the python collections not long ago

Steven Parker
Steven Parker
229,608 Points

What is it you are comparing to list.append()?

fahad lashari
fahad lashari
7,693 Points

Hi I am talking in regards to where he used += to add things into the list. Just wondering why he would use that instead of append and extend.

kind regards

2 Answers

Steven Parker
Steven Parker
229,608 Points

It depends on what you are adding to the list.

For single items, .append(), .extend(), and += all do the same thing.

But if the item being added is another list, there's a difference. Both .extend() and += will add the elements from the new list onto the other, but .append() will add the entire new list as a single element onto the other list.

Say for example, you had two lists each with 3 elements. If you combine them with .append() you will have a list with 4 elements, and the last element will itself be a list of 3 elements. But if you combine them with either of the other methods you will get a list of 6 individual elements.

Steven Parker
Steven Parker
229,608 Points

The inner list, yes. And the same with extend. Both would still be unwrapping the outer list and adding the elements individually.