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This Is Your Complete Guide To All Python List Methods

Aya Bouchiha
Full stack web developer
・4 min read

Hi, I'm Aya Bouchiha, today, I'm going to talk about the list of built-in objects.

Definition of a List

A list is a mutable, iterable, ordered collection of values. It is used to store different and multiple values in one variable.

Creating a list

new_list = ['hi', 1, False, {"name":"Aya"}, [10, 20], None]

print(new_list) # ['hi', 1, False, {"name":"Aya"}, [10, 20], None]
print(type(new_list)) # <class 'list'>
print(len(new_list)) # 6
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All list methods

append()

append(value): this list method lets you insert an element at the end of the list.

my_list = [10, 20, 30]

my_list.append(40)

print(my_list.append(50)) # None

print(my_list) # [10, 20, 30, 40, 50]

my_list.append() # error
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insert()

insert(index, value): used to add a new element at a given index

admins = ['Aya Bouchiha', 'John Doe']

admins.insert(0, 'Simon Bihao') 
print(admins)  # ['Simon Bihao', 'Aya Bouchiha', 'John Doe']

admins.insert(2, 'Salma Nouhary')
print(admins) # ['Simon Bihao', 'Aya Bouchiha', 'Salma Nouhary', 'John Doe']
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pop()

pop(index = -1): delete the elements that exist in the given index, by default the index is the -1 which is the index of the last element. In addition, it returns the deleted element.

admins = ['Aya Bouchiha', 'John Doe']
old_admin = admins.pop()

print(old_admin) # John Doe
print(admins) # ['Aya Bouchiha']


tasks = ['eat fruits', 'go to gym', 'drink water']
completed_task = tasks.pop(1)

print(completed_task) # go to gym
print(tasks) # ['eat fruits', 'drink water']
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remove()

remove(value): deletes the first item that matches the given value.

tasks = ['eat fruits', 'go to gym', 'drink water']
tasks.remove('eat fruits')

print(tasks.remove('drink water')) # None
print(tasks) # ['go to gym']
tasks.remove('something else') # error
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clear()

clear(): used to remove all list's items.

tasks = ['eat fruits', 'go to gym', 'drink water']

print(len(tasks)) # 3

tasks.clear()

print(tasks) # []
print(len(tasks)) # 0
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copy()

copy(): this list method is used to return a copy of the specified list.

today_tasks = ['eat fruits', 'go to gym', 'drink water']

tomorrow_tasks = today_tasks.copy()

print(tomorrow_tasks) #  ['eat fruits', 'go to gym', 'drink water']

today_tasks.clear()

print(today_tasks) # []

print(tomorrow_tasks) # ['eat fruits', 'go to gym', 'drink water']
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index()

index(value): returns the index of the first item that matched the given value.

today_tasks = ['eat fruits', 'go to gym', 'drink water']

print(today_tasks.index('eat fruits')) # 0
print(today_tasks.index('drink water')) # 2
print(today_tasks.index('buy a mouse')) # error
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count()

count(value): returns the number of repeated items that match the specified value in a list.

product_prices = [12, 227, 0, 54, 0, 20]
free_products_number = product_prices.count(0)

print(free_products_number) # 2
print(product_prices.count(224578)) # 0
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extend()

extend(iterable): helps you to insert an iterable(list, set,...) at the end of the specified list.

all_users = ['Yasm', 'Nopay', 'Houssam']
facebook_users = {'Aya', 'Simon'}
instagram_users = ('Ayman', 'Soha')

all_users.extend(facebook_users)
all_users.extend(instagram_users)

# ['Yasm', 'Nopay', 'Houssam', 'Simon', 'Aya', 'Ayman', 'Soha']
print(all_users)
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reverse()

reverse(): reverse the order of the specified list

marks = [15, 45, 51, 70]
marks.reverse()

print(marks) # [70, 51, 45, 15]
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sort()

sort(reverse = False, key(optional)): sort the list's items, if the reverse parameter was True, the items will be sorted in descending order.

the key parameter is used to specify a function that will specify the sorting criteria.

Example:1

marks = [7, 62, 71, 56, 24]
marks.sort()

print(marks) # [7, 24, 56, 62, 71]

marks.sort(reverse=True)

print(marks) # [71, 62, 56, 24, 7]

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Example:2

def get_marks(student: dict):
  return student.get('marks')

students = [
  {
    "name": "Aya Bouchiha",
    "email": "developer.aya.b@gmail.com",
    "marks": 92
  },
  {
    "name": "John Doe",
    "email": "john.doe@gmail.com",
    "marks": 95
  },
  {
    "name": "Ryan Hosm",
    "email": "ryan.hosm@gmail.com",
    "marks": 80
  }
]

students.sort(key=get_marks)

print(students)
# [{'name': 'Ryan Hosm', 'email': 'ryan.hosm@gmail.com', 'marks': 80}, {'name': 'Aya Bouchiha', 'email': 'developer.aya.b@gmail.com', 'marks': 92}, {'name': 'John Doe', 'email': 'john.doe@gmail.com', 'marks': 95}]

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Example3 (using lambda)

products = [
  {
    "name" : "laptop",
    "price": 500
  },
  {
    "name" : "phone",
    "price": 150
  },
  {
    "name" : "mouse",
    "price": 16
  },
  {
    "name": "keyboard",
    "price": 24
  }

]

products.sort(reverse=True, key=lambda product: product.get("price"))
print(products)

highest_price = products[0].get('price')
print(f'highest price is: {highest_price}')
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Output:

[{'name': 'laptop', 'price': 500}, {'name': 'phone', 'price': 150}, {'name': 'keyboard', 'price': 24}, {'name': 'mouse', 'price': 16}]
highest price is: 500
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Summary

  • append(value): inserts an element at the end of the list.

  • insert(index, value): adds a new element at a given index.

  • pop(index = -1): deletes the element that exist in the given index.

  • remove(value): deletes the first item that match the given value.

  • clear(): removes all list's items.

  • copy(): returns a copy of the specified list.

  • index(value): returns the index of the first item that matched the given value.

  • count(value): returns the number of repeated items that match the specified value in a list.

  • extend(iterable): inserts an iterable at the end of the specified list.

  • reverse(): reverses the order of the specified list.

  • sort(reverse = False, key(optional)): sorts the list's items.

References & useful Resources

Suggested posts

To Contact Me:

email:developer.aya.b@gmail.com
telegram: Aya Bouchiha

Hope you enjoyed reading this post :)

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