Python List Comprehensions

List comprehensions provide a concise way to create and transform lists in Python.

They are often faster and more readable than traditional for-loops.

1. Basic Syntax

A list comprehension consists of an expression followed by a for clause inside square brackets.

              
Python

          Basic syntax
        
[expression for item in iterable]

2. Creating a List

              
Python

          Generate squares of numbers
        
squares = [x * x for x in range(1, 6)]
print(squares)

Output: [1, 4, 9, 16, 25]

3. Adding Conditions

You can filter elements using an if condition.

              
Python

          Get even numbers only
        
evens = [x for x in range(1, 11) if x % 2 == 0]
print(evens)

Output: [2, 4, 6, 8, 10]

4. Working with Strings

              
Python

          Convert strings to uppercase
        
names = ['alice', 'bob', 'charlie']
upper_names = [name.upper() for name in names]
print(upper_names)

Output: ['ALICE', 'BOB', 'CHARLIE']

5. Nested List Comprehensions

              
Python

          Flatten a matrix
        
matrix = [[1, 2], [3, 4], [5, 6]]
flat = [num for row in matrix for num in row]
print(flat)

Output: [1, 2, 3, 4, 5, 6]

6. Using If-Else

              
Python

          Label numbers as even or odd
        
labels = ['Even' if x % 2 == 0 else 'Odd' for x in range(1, 6)]
print(labels)

Output: ['Odd', 'Even', 'Odd', 'Even', 'Odd']

7. Why Use List Comprehensions?

1. Cleaner and shorter code.

2. Better readability.

3. Often faster than traditional loops.

4. Widely used in data science and automation.

8. Practice Problems

1. Create a list of cubes from 1 to 20.

2. Extract vowels from a string.

3. Flatten a nested list.

4. Create a list of positive numbers from a mixed list.