187 – Anatomy of a list comprehension

187 – Anatomy of a list comprehension#

A list comprehension is made up of three sections:

Data transformation: The code that is transforming elements by applying a function or another expression to your values.
Data source: If you’re transforming data, the data must come from somewhere.
Data filter: Optionally, you can add a data filter so you’re only transforming some of the elements coming from the data source.

These three parts make up a general list comprehension. In code, it looks like this:

my_list = [
    data_transformation(value)  # 1
    for value in data_source    # 2
    if predicate(value)         # 3
]

Each line of the list comprehension above maps to one of the sections of a list comprehension. Here is a concrete example:

my_list = [
    n ** 2                           # 1
    for n in range(1000)             # 2
    if (n % 3 == 0) or (n % 5 == 0)  # 3
]

The list comprehension above