Python List Comprehension

List comprehension offers a shorter syntax for creating a new list based on the values of an existing list.

With list comprehension, you can create a new list using a single line of code.

Syntax

newlist = [expression for item in iterable if condition]

• expression – The value to include in the new list.
• item – The current item in the iteration.
• iterable – The sequence to loop through.
• condition – Optional filter.

Without List Comprehension

Example:

fruits = ["apple", "banana", "cherry", "kiwi"]

newlist = []

for x in fruits:
    if "a" in x:
        newlist.append(x)

print(newlist)

Output:

['apple', 'banana']

With List Comprehension

Example:

fruits = ["apple", "banana", "cherry", "kiwi"]

newlist = [x for x in fruits if "a" in x]

print(newlist)

Output:

['apple', 'banana']

Condition in List Comprehension

Only include items that meet a condition.

Example:

numbers = [1, 2, 3, 4, 5, 6]

even_numbers = [x for x in numbers if x % 2 == 0]

print(even_numbers)

Output:

[2, 4, 6]

No Condition

You can copy a list without using a condition.

Example:

fruits = ["apple", "banana", "cherry"]

newlist = [x for x in fruits]

print(newlist)

Output:

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

Using an Expression

The expression can modify items before adding them to the new list.

Example:

fruits = ["apple", "banana", "cherry"]

newlist = [x.upper() for x in fruits]

print(newlist)

Output:

['APPLE', 'BANANA', 'CHERRY']

Mathematical Operations

Example:

numbers = [1, 2, 3, 4, 5]

squares = [x * x for x in numbers]

print(squares)

Output:

[1, 4, 9, 16, 25]

Using range()

Example:

numbers = [x for x in range(5)]

print(numbers)

Output:

[0, 1, 2, 3, 4]

Using range() with Condition

Example:

numbers = [x for x in range(10) if x < 5]

print(numbers)

Output:

[0, 1, 2, 3, 4]

If Else in List Comprehension

Example:

numbers = [1, 2, 3, 4, 5]

result = ["Even" if x % 2 == 0 else "Odd" for x in numbers]

print(result)

Output:

['Odd', 'Even', 'Odd', 'Even', 'Odd']

Practical Example

Create a list of names longer than 4 characters.

Example:

names = ["John", "David", "Sam", "Michael"]

result = [name for name in names if len(name) > 4]

print(result)

Output:

['David', 'Michael']

Benefits of List Comprehension

• Shorter and cleaner code.
• Faster than traditional loops in many cases.
• Easy to read and maintain.
• Useful for filtering and transforming data.

Summary

• List comprehension provides a concise way to create lists.
• It can replace simple for loops.
• Conditions can be added using if.
• Expressions can modify values during creation.
• It is commonly used for filtering and transforming data.