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What Is the Difference Between Python's List Methods Append and Extend?

Sarah Jenkins • • 15 min read
What Is the Difference Between Python's List Methods Append and Extend?

What's the difference between the list methods append() and extend()?

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20 Answers

append appends a specified object at the end of the list:

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

extend extends the list by appending elements from the specified iterable:

>>> x = [1, 2, 3]
>>> x.extend([4, 5])
>>> print(x)
[1, 2, 3, 4, 5]
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append adds an element to a list. extend concatenates the first list with another list/iterable.

>>> xs = ['A', 'B']
>>> xs
['A', 'B']

>>> xs.append("D")
>>> xs
['A', 'B', 'D']

>>> xs.append(["E", "F"])
>>> xs
['A', 'B', 'D', ['E', 'F']]

>>> xs.insert(2, "C")
>>> xs
['A', 'B', 'C', 'D', ['E', 'F']]

>>> xs.extend(["G", "H"])
>>> xs
['A', 'B', 'C', 'D', ['E', 'F'], 'G', 'H']
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What is the difference between the list methods append and extend?

  • append adds its argument as a single element to the end of a list. The length of the list itself will increase by one.
  • extend iterates over its argument adding each element to the list, extending the list. The length of the list will increase by however many elements were in the iterable argument.
Sarah Jenkins
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Sarah Jenkins

Sarah Jenkins is a veteran tech journalist with over 12 years of experience covering artificial intelligence, mobile innovations, and digital ethics. Her insights have appeared in leading technology publications worldwide.