Lesson 1: Variables, Types and Everything Nice

The Bread and Butter of Every Program

Variables. . . Everything's A Variable

In programming, variables, much like in mathematics, hold information. They can be assigned, or given a value, manipulated, typically with math, or re-assigned to replace or change values.

Python considers anything after a single equal sign to be variable assignment or re-assignment, if applicable.

example.py

    the_meaning_of_life = 42
    favorite_beverage = "Coffee"
    is_easy = True

The Python Convention for naming variables is to use snake case, or all lowercase letters with words separated with underscores.

Variables that represent constants, or values that are meant to never change, are typically written with all uppercases with words also separated with underscores.

Notice that there is a line break after every line of code. Python is a programming language where this is important. The computer needs to know where one line ends and another begins, which is what line breaks are for. Think of each line as a sentence with a command that the computer will execute. You wouldn't want to confuse two sentences together or you might get unexpected results, but you also want to keep your sentences short and concise.

In the above example, 3 different variables are assigned to 3 different pieces of information. Let's take a deeper look at what's happening piece by piece. In Python, everything that is followed by a # is considered a comment. Comments are used to annotate code and are ignored by the Python Interpreter.

example.py

    # Here, we are assigning the variable, the_meaning_of_life, to the number, an integer to be exact, 42.
    the_meaning_of_life = 42

    # A number isn't very useful for determining your beverage of choice, so let's use something called a string instead.
    favorite_beverage = "Coffee"

    # Something is either easy or it's not, so let's use a boolean value for that.
    is_easy = True

    # All of these variables are assigned to types.

Types of Types

Data Types are the classifications of information that variables can hold. They are the simplest form of data and are built into the language. These types are the backbone of every program and you will use them for any logic that you program.

Here are the basic data types:

Strings

Strings are characters, words, sentences, and anything in between. They are created using matching single quotes (') or double quotes (") wraping around text.

strings.py

    # This is a string using double quotes.
    question = "What programming language are you going to master?"

    # This is a string using single quotes.
    answer = 'Python'

    # If a string starts with a double quote it will end at the next double quote. Same for single quotes.

    # But what if you need to use the characters ' or " in your string?
    # We can use the forward slash character (\) to escape special characters so we can use them in strings!
    quote = "\"Isn't Python so Easy\" said John."

While you can use any mixture of single quote and double quote strings in your programs, it is best practice to maintain a uniform style for strings. This course will use double quotes for all strings going forward.

Integers

Integers are numbers without a decimal place. Integers are not wrapped with quotes, rather they stand alone.

integers.py

    # This is an integer.
    luckiest_number = 13

    # This is also an integer.
    favorite_number = 4

Floats

If need to work with numbers that have decimals, we use floats.

Floats are numbers with a decimal place. Like integers, they too are not wrapped with quotes.

floats.py

    # This is a float.
    pi = 3.1415926

    # This is also a float.
    price = 10.99

    # While this may appear to be an integer, since it has a trailing decimal, it is a float.
    temperature = 30.0

Booleans

Computers are giant logic boxes. Thus, we need something to determine logical flow. That's where booleans come in.

Booleans are logical values that can only either be True or False.

booleans.py

    # This variable is defined as true.
    is_adult = True

    # This variable is defined as false.
    is_child = False

More Complex Data Types

These types build upon the basic data types, and allow for more complex data structures. These are useful in keeping organized data together.

Lists

Lists are ordered collections of any data type. They can contain strings, integers, floats, other lists, etc. in any combination. Lists are created using matching square brackets ([ ]), with list entries separated by commas.

Other programming languages may call lists Arrays, which are lists which have an enforced type. This means that arrays may not contain 2 different types, like an integer and a string. Python does not have a built-in array type (outside of libraries, explained in future lessons). Simply put, arrays can be seen as lists in Python.

lists.py

    # This is a list of strings.
    dwarves = ["Sneezy", "Sleepy", "Happy", "Doc", "Grumpy", "Dopey", "Bashful"]

    # This is a list of integers, strings, and floats.
    wallet = [5, 0.25, 0.25, "Credit Card", 0.05, "Drivers License"]

    # Notice that entries in lists are not unique and can be used multiple times.

Dictionaries

Dictionaries are a collection of key-value pairs.

In a ```key-value`` pair, the key represents a unique reference to a value. Each key is tied to a value, and values are retrieved through the key. Values can be any data type, including dictionaries.

Dictionaries can be created using braces ({ }), with key value pairs separated by commas. The pairs themselves are represented by the left and right of a colon (:). The left represents the key and the right represents the value.

dictionaries.py

    # This is a dictionary with strings as keys and integers/floats for values.
    price_ledger = {
        "Milk": 3,
        "Eggs": 2,
        "Flour": 1.5
    }

    # This is a dictionary with nested dictionaries and lists.
    teams = {
        # There can only be one West University team.
        "West University": {
            # That team can only have one list of players.
            "players": [
                # Here are the players.
                "Steve",
                "Alan",
                "Rob"
            ]
        },
        # Likewise, there can only be one North College team.
        "North College": {
            # That team also has a list of players.
            "players": [
                # And here are their players.
                "Jason",
                "Derrick",
                "John"
            ]
        }
    }

Don't worry if all of this information feels overwhelming. This lesson is simply a brief introduction to these types. All of these data types will each have their own in-depth lessons where properties, use cases, and working with types, will be explained in greater depth.

The next article is a series of exercises where you will be working with data types in your IDE. You will get a better understanding the more you work with them.