In a list, what is the difference between append and extend?

Question

Num list in Python, there are the methods append and extend.

What’s the difference between them and when to use each?

Answer 1

extend()

Gets a "iterable" as parameter and extends the list by adding its elements

lista = [1, 2, 3]
lista.extend([4, 5])
print(lista) 
# Saída: [1, 2, 3, 4, 5]

append()

adds an element at the end of the list

lista = [1, 2, 3]
lista.append([4, 5])
print(lista) 
# Saída: [1, 2, 3, [4, 5]]

Answer 2

In the append() you add elements to the end of the list, in extend() a iterable as argument, and this argument is added to the end of the element-by-element list.

If you have a list and want to include elements from another list in it, you should use the extend(); otherwise it will add a list at the end of your list.

Example:

lista1 = [1, 2, 3]
lista1.append([4, 5])
print lista1
# resultado: [1, 2, 3, [4, 5]]

lista2 = [1, 2, 3]
lista2.extend([4, 5])
print lista2
# resultado: [1, 2, 3, 4, 5]

lista3 = [1, 2, 3]
lista3.append(4)
print lista3
# resultado: [1, 2, 3, 4]

See working on Ideone.

Answer 3

• append will add any list as an item

  foo = [1, 2, 3]
  foo.append([4, 5])
  print foo
  

  Returns: [1, 2, 3, [4, 5]]

• extend the elements would be almost like a "merge"

  foo = [1, 2, 3]
  foo.extend([4, 5])
  print foo
  

  Returns: [1, 2, 3, 4, 5]

Of Soen: https://stackoverflow.com/a/252711/1518921

Example in the ideone: http://ideone.com/2EgMan