1 What is Considered Basic?

When I work in Python, I generally focus on three core (fundamental) data structures (or specialized variations from the collections module).

Take note of the correspondence to C++ and Java. While you will encounter generators and tuples in Python… they will be defined in the latter part of this lecture.

1.1 list

A list is a collection of values. We could have a list of prime numbers…

prime_numbers = [1, 2, 3, 5, 7, 11, 13, 17, 19]

or names…

names = ["Thomas", "Jay", "Joe"]

Python lists are not restricted to storing a single type of data. For example, we can store a string and a float in the same list.

random_things = ["Python", 3.11]

1.2 set

A set is similar to a list, except entries must be unique. If we were to store a bunch of colors…

some_colors = {"Blue", "Red", "Green", "Cyan", "Teal"}
some_colors.add("Blue")
some_colors.add("Red")
some_colors.add("Teal")

the last three lines would have no effect, since "Blue", "Red", and "Teal" are already in the set.

1.3 dict

The usual definition of a dict (what Java would call a HashMap and C++ would call an unordered_map) is…

A dictionary (hashmap) is a collection of key-value pairs where each entry can be located in amortized constant time.

We can think of a dict as a lookup table where finding a value can be done quickly. Suppose you needed to track the favourite colors for a group of people…

favourite_colors = {
    "Thomas": "Blue",
    "Jessica": "Purple",
    "Angela": "Pink"
}

We could retrieve and print my (Thomas’s) favorite color with…

print(favourite_colors["Thomas"])

We can think of a dict as an array where the index can be a key that we want to match to some value.

2 What is a Generator?

A generator is a lazily-evaluated list. Unlike a list where all the values are known, a generator’s values are computed on demand.

For example, the list…

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

contains the values 1 through 10 and uses 10 ints worth of space. Imagine if we had one (1) billion numbers. A generator expression defines how to create (or construct) each value, but only creates a value when specifically asked to do so.

The range function is one such generator. Consider the following snippet.

numbers = range(1, 100)

print(next(numbers))
print(next(numbers))
print(next(numbers))

The snippet would generate (as output)…

1
2
3

The remaining values would never be generated. A generator is ideal when we do not need every value all at once. You have seen this with the Python for loop…

for num in range(1, 100):
    print(num)

We want to loop output the numbers 1 through 99 one at a time. Not only do we only need one number at a time… once we have output each number we can discard it.

3 What is a Tuple?