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2. Data Structures

List

A data structure is something we use to store values. A list is an important in-built data structure in python, which we represent using square brackets:

my_list = [1, 2, 3, 4, 5]

We can access the contents of a list using indices, just like we did for strings. Remember that we start counting from 0. We can also find the length of the list using len. Lastly, we can also slice a list to retrieve a smaller portion of the list by using [start:end], where start is the starting index (inclusive), and end is the ending index (non-inclusive).

my_list = [1, 2, 3, 4, 5]
number = my_list[3]      # number = 4
length = len(my_list)    # length = 5
new_list = my_list[2:4]  # new_list = [3, 4]

Dictionary

Another useful data structure is called a dictionary.

my_dict = {'a': 1, 'b': 2, 'c': 3}

A dictionary contains entries which are key-value pairs. In the example above, a : 1 is a key-value pair where a is the key and 1 is the value. Just like in a normal dictionary, we can lookup a dictionary to retrieve the corresponding value of a key as such:

my_dict = {'a': 1, 'b': 2, 'c': 3}
number = dic['b']  # number = 2

We can also add an entry to the dictionary as such:

my_dict['d'] = 4