[Python] Slicing Lists

In addition to accessing individual elements from a list we can use Python's slicing notation to access a subsequence of a list. Consider this list of months,

months = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']

We can slice the third quarter of the year from the months list like this:

>>> q3 = months[6:9]
>>> print(q3)
['July', 'August', 'September']
>>> print(months)
['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']

There are a couple of slicing shortcuts that simplify common situations. If you would like to make a slice that begins at the very beginning of the original list, or that ends at the very end of the original list, you can omit the start or end index like this:

>>> first_half = months[:6]
>>> print(first_half)
['January', 'February', 'March', 'April', 'May', 'June']
>>> second_half = months[6:]
>>> print(second_half)
['July', 'August', 'September', 'October', 'November', 'December']