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Python Introducing Lists Meet Lists Addition

Posted by Perfect Storm
Perfect Storm
1,416 Points

What's the difference between append and extend in this example?

I don't understand what differentiates append and extend. Is it that append is for one item as a string and extend is for adding multiple items?

Dave StSomeWhere
Dave StSomeWhere
19,870 Points
Dave StSomeWhere
Dave StSomeWhere
19,870 Points

It is possible that if you try experimenting in your REPL you might get a better understanding of the difference between the two methods.

Something like below could be a good start:

list1 = ['a', 'b', 'c']
list2 = ['d','e', 'f']
list3 = [1, 2, 3]
str1 = "String Example"
dict1 = {'name':'dict one', 'type':'sample'}
dict2 = {'name':'dict two', 'type':'another sample'}
list1.append(list2)
list1
['a', 'b', 'c', ['d', 'e', 'f']]
list1.extend(list3)
list1
['a', 'b', 'c', ['d', 'e', 'f'], 1, 2, 3]
list1.extend(dict1)
list1
['a', 'b', 'c', ['d', 'e', 'f'], 1, 2, 3, 'name', 'type']
list1.append(dict2)
list1
['a', 'b', 'c', ['d', 'e', 'f'], 1, 2, 3, 'name', 'type', {'name': 'dict two', 'type': 'another sample'}]

2 Answers

Steven Parker
Steven Parker
231,271 Points
Steven Parker
Steven Parker
231,271 Points

The "append" method adds a single item to a list, though the item might be another list. On the other hand, "extend" will add another list as individual items. You can see this in the example you provided:

list1.append(list2)
list1
['a', 'b', 'c', ['d', 'e', 'f']]           # list2 is still a list, INSIDE the big list
list1.extend(list3)
list1
['a', 'b', 'c', ['d', 'e', 'f'], 1, 2, 3]  # but 1, 2, and 3 are separate in the big list

Happy coding! :christmas_tree: And for some holiday-season fun and coding practice, give Advent of Code a try! :santa:

nicolaspeterson
nicolaspeterson
8,569 Points

Was just about to ask the same question and found your answer. Many thanks.

aaron r
aaron r
1,669 Points
aaron r
aaron r
1,669 Points

if one can extend a list with single list item, why bother with append?

Steven Parker
Steven Parker
231,271 Points
Steven Parker
Steven Parker
231,271 Points

You might want to add something to a list that isn't already in another list.