Python - append vs. extend

append: Appends object at end

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

gives you: [1, 2, 3, [4, 5]]

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extend: extends list by appending elements from the iterable

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

gives you: [1, 2, 3, 4, 5]