Python List Append vs Extend – Performance Comparison

In this article, we will discuss python list append and extend functions. We’ll also check the performance of the functions.

List append

The append function is used to add an item to the end of the list.

The syntax of append function

list.append(x)

Examples

Add a single item to list

languages = ["English","French","Hindi"]
languages.append("Spanish")
print(languages)

Output

['English', 'French', 'Hindi', 'Spanish']

Add multiple items to the list. We can loop and add items to the list. ( We can also use extend function)

languages = ["English","French","Spanish"]
ind_languages = ["Tamil","Hindi"]

for language in ind_languages:
  languages.append(language)

print(languages)

Output

['English', 'French', 'Spanish', 'Tamil', 'Hindi']

Append list to the end of the list

languages = ["English","French","Spanish"]
ind_languages = ["Tamil","Hindi"]

languages.append(ind_languages)

print(languages)

Output

['English', 'French', 'Spanish', ['Tamil', 'Hindi']]

List extend

The list extend function is used to extend a list by appending all the items from iterable.

Syntax of list extend

list.extend(iterable)

Examples

To append a sublist of items to another list we can use the extend function.

languages = ["English","French","Spanish"]
ind_languages = ["Tamil","Hindi"]

languages.extend(ind_languages)

print(languages)

Output

['English', 'French', 'Spanish', 'Tamil', 'Hindi']

Which is method is faster?

To add another list either we can use these functions. Let’s compare the speed of these functions.

Let’s create a list of 100 numbers and add 1000 items to it.

import time

x = list(range(1, 101))
y = list(range(2000,3001 ))

start= time.time()
x.extend(y)
elapsed= time.time()- start

print( f"Elapsed time  : {elapsed} sec")

Output

Elapsed time  : 9.036064147949219e-05 sec

Lets loop and add items using append

import time

x = list(range(1, 101))
y = list(range(2000,3001 ))

start= time.time()

for z in y:
  x.append(z)

elapsed= time.time()- start
print( f"Elapsed time  : {elapsed} sec")

Output

Elapsed time  : 0.00475311279296875 sec

From this, we can see that extend the function is much faster than append. If we want to add a list of items to another list we can use extend function.

Conclusion

In conclusion, list append and extend are useful functions. To add a single item we can use the append function and we can use the extend function to add sub-list items. You can read about list len function performance here.