In addition to sequence operations and list methods, Python includes a more advanced operation called a list comprehension.
List comprehensions allow us to build out lists using a different notation. You can think of it as essentially a one line for loop built inside of brackets. For a simple example:
# Grab every letter in string
lst = [x for x in 'word']
# Check
lst
['w', 'o', 'r', 'd']
This is the basic idea of a list comprehension. If you're familiar with mathematical notation this format should feel familiar for example: x^2 : x in { 0,1,2...10}
Lets see a few more example of list comprehensions in Python:
# Square numbers in range and turn into list
lst = [x**2 for x in range(0,11)]
lst
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
Lets see how to add in if statements:
# Check for even numbers in a range
lst = [x for x in range(11) if x % 2 == 0]
lst
[0, 2, 4, 6, 8, 10]
Can also do more complicated arithmetic:
# Convert Celsius to Fahrenheit
celsius = [0,10,20.1,34.5]
fahrenheit = [ ((float(9)/5)*temp + 32) for temp in Celsius ]
fahrenheit
[32.0, 50.0, 68.18, 94.1]
We can also perform nested list comprehensions, for example:
lst = [ x**2 for x in [x**2 for x in range(11)]]
lst
[0, 1, 16, 81, 256, 625, 1296, 2401, 4096, 6561, 10000]
Later on in the course we will learn about generator comprehensions. After this lecture you should feel comfortable reading and writing basic list comprehensions.