Lists

Updated Oct 28, 2019 ·

Lists

Lists are ordered containers that hold multiple items. They are mutable, so you can add, remove, or update items easily.

In the example below, we create a cookies list of and manipulate it:

cookies = ["chocolate chip", "oatmeal", "sugar"]

# Add a new cookie
cookies.append("peanut butter")

# Combine with another list
more_cookies = ["ginger", "snickerdoodle"]
cookies.extend(more_cookies)

# Print the list
print(cookies)

Output:

['chocolate chip', 'oatmeal', 'sugar', 'peanut butter', 'ginger', 'snickerdoodle']

You can access a specific item by its index:

# Print the third cookie
print(cookies[2])

Output:

sugar

Common List Operations

Get the number of elements using len():

fruits = ["apple", "banana", "cherry"]
print(len(fruits))

Output:

Loop over each element in a sequence:

for fruit in fruits:
    print(fruit)

Output:

apple
banana
cherry

Check if an element exists in a sequence:

if "banana" in fruits:
    print("Found banana!")

Output:

Found banana!

Access an element by index:
```
print(fruits[1])
```
Output:
```
banana
```

Get a slice of a sequence:

print(fruits[0:2])  # first two elements
print(fruits[:2])   # same as above
print(fruits[1:])   # from second element to end

Output:

['apple', 'banana']
['apple', 'banana']
['banana', 'cherry']

Loop over indexes and elements together with enumerate():

for i, fruit in enumerate(fruits):
    print(i, fruit)

Output:

apple
banana
cherry

Replace an element at a specific index:

fruits[1] = "blueberry"
print(fruits)

Output:

['apple', 'blueberry', 'cherry']

Add an element to the end with append():

fruits.append("orange")
print(fruits)

Output:

['apple', 'blueberry', 'cherry', 'orange']

Insert an element at a specific position with insert():

fruits.insert(1, "kiwi")
print(fruits)

Output:

['apple', 'kiwi', 'blueberry', 'cherry', 'orange']

Remove an element by index with pop():

removed = fruits.pop(2)
print(removed)
print(fruits)

Output:

blueberry
['apple', 'kiwi', 'cherry', 'orange']

Remove the first occurrence of a value with remove():

fruits.remove("kiwi")
print(fruits)

Output:

['apple', 'cherry', 'orange']

Sort the list in ascending order with sort():

fruits.sort()
print(fruits)

Output:

['apple', 'cherry', 'orange']

Reverse the order of elements with reverse():

fruits.reverse()
print(fruits)

Output:

['orange', 'cherry', 'apple']

Remove all elements with clear():
```
fruits.clear()
print(fruits)
```
Output:
```
[]
```

Create a shallow copy with copy():

fruits = ["apple", "banana"]
fruits_copy = fruits.copy()
print(fruits_copy)

Output:

['apple', 'banana']

Append all elements from another list with extend():

more_fruits = ["kiwi", "mango"]
fruits.extend(more_fruits)
print(fruits)

Output:

['apple', 'banana', 'kiwi', 'mango']

List Comprehension

List comprehensions are a compact way to create new lists from existing sequences. They let you apply expressions and conditions in a single line.

Basic: Creates new list by evaluating the expression for each element in the sequence.
```
squares = [x**2 for x in range(5)]  # [0, 1, 4, 9, 16]
```

With Condition: Adds elements to the new list only if the condition is met.

evens = [x for x in range(10) if x % 2 == 0]  # [0, 2, 4, 6, 8]

For more information, please see List Comprehensions.

Lists​

Common List Operations​

List Comprehension​

Lists

Common List Operations

List Comprehension