# 5.12 List Comprehensions¶

- Concise way to create new lists.
- Replaces using `for` to iterate over a sequence and create a list.

In [1]:

    list1 = []

In [2]:

    for item in range(1, 6):
        list1.append(item)

In [3]:

    list1

Out[3]:

    [1, 2, 3, 4, 5]

### Using a List Comprehension to Create a List of Integers¶

In [4]:

    list2 = [item for item in range(1, 6)]

In [5]:

    list2

Out[5]:

    [1, 2, 3, 4, 5]

- `for` clause iterates over the sequence produced by `range(1, 6)`.
- For each `item`, the list comprehension evaluates the expression to the left of the `for` clause and places the expression’s value in the new list.

### Mapping: Performing Operations in a List Comprehension’s Expression¶

- Mapping is a common functional-style programming operation that produces a result with the same number of elements as the original data being mapped.

In [6]:

    list3 = [item ** 3 for item in range(1, 6)]

In [7]:

    list3

Out[7]:

    [1, 8, 27, 64, 125]

### Filtering: List Comprehensions with `if` Clauses¶

- Another common functional-style programming operation is filtering elements to select only those that match a condition.
- Typically produces a list with fewer elements than the data being filtered.

In [8]:

    list4 = [item for item in range(1, 11) if item % 2 == 0]

In [9]:

    list4

Out[9]:

    [2, 4, 6, 8, 10]

### List Comprehension That Processes Another List’s Elements¶

- The `for` clause can process any iterable.

In [10]:

    colors = ['red', 'orange', 'yellow', 'green', 'blue']

In [11]:

    colors2 = [item.upper() for item in colors]

In [12]:

    colors2

Out[12]:

    ['RED', 'ORANGE', 'YELLOW', 'GREEN', 'BLUE']

In [13]:

    colors

Out[13]:

    ['red', 'orange', 'yellow', 'green', 'blue']

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