labs/Module-2/3.Statements/06-List Comprehensions.ipynb

List Comprehensions

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:

Example 1

In [ ]:

# Grab every letter in string
lst = [x for x in 'word']

In [ ]:

# Check
lst

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 }

Let's see a few more examples of list comprehensions in Python:

Example 2

In [ ]:

# Square numbers in range and turn into list
lst = [x**2 for x in range(0,11)]

In [ ]:

lst

Example 3

Let's see how to add in if statements:

In [ ]:

# Check for even numbers in a range
lst = [x for x in range(11) if x % 2 == 0]

In [ ]:

lst

Example 4

Can also do more complicated arithmetic:

In [ ]:

# Convert Celsius to Fahrenheit
celsius = [0,10,20.1,34.5]

fahrenheit = [((9/5)*temp + 32) for temp in celsius ]

fahrenheit

Example 5

We can also perform nested list comprehensions, for example:

In [ ]:

lst = [ x**2 for x in [x**2 for x in range(11)]]
lst

Later on in the course we will learn about generator comprehensions. After this lecture you should feel comfortable reading and writing basic list comprehensions.

In [ ]:

In [ ]: