📷 List comprehensions are a powerful and concise way to create lists in Python. They are a neat way to generate lists by applying operations to each element of a collection in a single line of code. With list comprehensions, you can create lists in a fraction of the time it would take with traditional loops, and your code will be much easier to read.
Let’s say you want to create a list of the squares of the first 10 numbers. Here’s how you would do it with a for loop:
squared_numbers = []
for i in range(1, 11):
squared_numbers.append(i**2)
Now, here’s the same thing using a list comprehension:
squared_numbers = [i**2 for i in range(1, 11)]
As you can see, the list comprehension is much cleaner and easier to read. With just one line of code, you can create a list of the squares of the first 10 numbers.
List comprehensions can also be used with conditions. For example, if you want to create a list of the squares of only the odd numbers in the range 1-10, you can use the following list comprehension:
squared_odd_numbers = [i**2 for i in range(1, 11) if i % 2 != 0]
In this case, the list comprehension uses the if clause to only add the square of an odd number to the list.
List comprehensions can also be used to create lists from existing lists. For example, if you have a list of numbers and you want to create a new list with only the positive numbers, you can use the following list comprehension:
numbers = [-2, -1, 0, 1, 2]
positive_numbers = [x for x in numbers if x > 0]
In this example, the list comprehension iterates through the numbers list and adds only the positive numbers to the positive_numbers list.
Here’s another example to flatten a 2D list:
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flattened_matrix = [num for row in matrix for num in row]
In this example, the matrix is a 2D list with three rows and three columns. The nested for loop in the list comprehension iterates through each row of the matrix and then through each number in that row.
The nested for loop in the list comprehension is equivalent to the following code:
flattened_matrix = []
for row in matrix:
for num in row:
flattened_matrix.append(num)
In conclusion, list comprehensions are a fun and easy way to create lists in Python. They make your code clean, concise, and easy to read. So the next time you need to create a list, give list comprehensions a try! Your code will thank you for it.