 # List Comprehensions

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
```
Out:
`['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 }

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
```
Out:
`[0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100]`

## 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
```
Out:
`[0, 2, 4, 6, 8, 10]`

## 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
```
Out:
`[32.0, 50.0, 68.18, 94.1]`

## 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
```
Out:
`[0, 1, 16, 81, 256, 625, 1296, 2401, 4096, 6561, 10000]`
In :
```for x in range(11):
for x in [x ** 2]:
lst = []
lst.append(x ** 2)
lst
```
Out:
``

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