List Comprehension

 

What You'll Learn: In this tutorial, you'll discover how to create a new list based on the values of an existing list using list comprehension. It's a shorter and more readable way to handle lists!

What is List Comprehension?

List comprehension offers a compact way to create lists. It can make your code cleaner and easier to read.

Example: Filtering Fruits

Imagine you have a list of fruits and you want to create a new list with only the fruits that have the letter "a" in their names.

Without List Comprehension:

python
fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = []
for x in fruits:
    if "a" in x:
        newlist.append(x)
print(newlist)

Output: ["apple", "banana", "mango"]

With List Comprehension:

python
fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = [x for x in fruits if "a" in x]
print(newlist)

Output: ["apple", "banana", "mango"]

Syntax of List Comprehension

python
newlist = [expression for item in iterable if condition]
  • expression: The current item in the iteration, which is the outcome.
  • item: The current item in the iterable.
  • iterable: An object like a list, tuple, set, etc.
  • condition (optional): A filter that only accepts items that evaluate to True.

Examples

  1. Filter Items:

    • Only accept items that are not "apple".
    python
    fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = [x for x in fruits if x != "apple"]
print(newlist)

    Output: ['banana', 'cherry', 'kiwi', 'mango']
     

  2. Iterable Example:

    • Use the range() function to create an iterable.
    python
    newlist = [x for x in range(10)]

    Output: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
     

  3. Condition Example:

    • Accept only numbers lower than 5.
    python
    newlist = [x for x in range(10) if x < 5]

    Output: [0, 1, 2, 3, 4]
     

  4. Manipulate Outcome:

    • Set the values in the new list to upper case.
    python
    newlist = [x.upper() for x in fruits]

    Output: ['APPLE', 'BANANA', 'CHERRY', 'KIWI', 'MANGO']
     

    • Set all values in the new list to 'hello'.
    python
    newlist = ['hello' for x in fruits]

    Output:  ['hello', 'hello', 'hello', 'hello', 'hello']
     

  5. Conditional Expression:

    • Return "orange" instead of "banana".
    python
    newlist = [x if x != "banana" else "orange" for x in fruits]

    Output: ['apple', 'orange', 'cherry', 'kiwi', 'mango']
     

Try It Yourself: Fun Exercises

  1. Filter Your Favorite Colors:
    • Create a list of colors.
    • Use list comprehension to create a new list with colors containing the letter "e".
  2. Number Manipulation:
    • Create a list of numbers from 1 to 20.
    • Use list comprehension to create a new list with only even numbers.

Summary:

In this Python tutorial, we learned how to use list comprehension to create new lists based on existing ones. This method offers a concise and readable way to filter and manipulate list items. Keep experimenting and have fun with list comprehension in Python!