Below are some notes I took when first learning Python list comprehension. They have come in handy many times.

For each example, I show how it would be completed using a for loop and how it would be completed using list comprehension.

Example 1: Copy items from one list to another

``````nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

# Make a new list with the same elements of nums
new_list = []

for i in nums:
new_list.append(i)

print(new_list)

# Make a new list with the same elements of nums
new_list2 = [i for i in nums]
print(new_list2)``````

Example 2: Double to values in list one and add them to a new list

``````nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

# Make a new list with the each of the elements doubled
new_list = []

for i in nums:
new_list.append(i * 2)

print(new_list)

# Make a new list with the each of the elements doubled
new_list2 = [i*2 for i in nums]
print(new_list2)``````

Example 3: Create a new list with the squares of the even items

``````nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

# Make a new list with the squares of the even numbers
new_list = []

for i in nums:
if (i % 2 == 0):
new_list.append(i*i)

print(new_list)

# Make a new list with the each of the elements doubled
new_list2 = [i*i for i in nums if i % 2 == 0]
print(new_list2)``````

Example 4: Create a (letter, number) pair for each letter in 'wxyz' and each number in '9876'

``````# Create a (letter, number) pair for each letter in 'wxyz' and each number in '9876'
new_list = []
for letter in 'wxyz':
for number in range(9, 5, -1):
new_list.append((letter, number))

print(new_list)

new_list = [(letter, number) for letter in 'wxyz' for number in range(9, 5, -1)]
print(new_list)``````