Python Comments, Operations, and Variables

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In this lesson, we will be discussing the very basics of Python. Specifically, we will discuss comments, operations, and variables in the Python programming language.

The Basics of Comments in Python (or any other language!)

In computer programming, comments are text included in your code that is not actually run by the computer. Comments exist to instruct humans; the rest of the code exists to instruct computers.

To start our course, I’ll explain how you can put comments in your code. Throughout the rest of this course, I will include comments after blocks of code to explain what the output of the code should be.

Single-Line Comments in Python

Most programming languages (Python included) have slightly different syntax for single- and multi-line comments. The single-line comment operator in Python is the hash character ‘#’.

You can see an example of a single-line Python comment below:

#This is a comment in Python

This means that the entire line that starts with ‘#’ will not be executed by the Python compiler or interpreter (which is fancy language that means this line will not run as part of the code).

Multi-Line Comments in Python

Multi-line comments in Python are initiated and completed using three quotes (can be single or double quotes):











This means that any code after the first “”” and before the second “”” will not be executed by the Python compiler or interpreter.

Multi-line comments are often used at the beginning of function declarations to describe the purpose of a function. We have not yet explored functions in this course, but an example of a multi-line comment in a Python function is below:

def my_function(name):


    This function prints the name passed in as an argument.



You may also sometimes see block comments, which serve to visibly chunk up your code into manageable blocks. Block comments start and end with a line of hash characters. An example is below:


#This is a block comment!


Basic Math Operations in Python

Now that we have a basic understanding of comments in the Python programming language, let’s continue by discussing basic math operations in Python.

Since Python is primarily used by scientists and other quantitatively-oriented programmers, these fundamental math operations are extremely, extremely important. Let’s dig in!


As you’d guess, you can add two numbers in Python using the ‘+’ character:

2 + 2

#returns 4

You can chain multiple addition operators together, just as you can in conventional mathematics. An example is below:

2 + 3 + 5

#returns 10


Similar to addition, the subtraction operator in Python is exactly what your intuition would suggest. Subtraction is performed using the ‘-’ character in Python:

2 - 1

#returns 1

Like addition, subtraction operations can be chained together. An example is below:

10 - 2 - 3

#returns 5


In Python, multiplication is performed using the asterisk, or *. An example is below:

2 * 2

#returns 4

As with the other math operators, multiplication operations can be chained together. An example is below:

2 * 3 * 4

#returns 12


Division is performed in Python using the forward slash ‘/’. For example, if you want to divide 6 by three, you’d do so using the following code:

6 / 3

#returns 2

Division can also be chained together like the other operators we’ve discussed, but you’ll want to be careful that the order of operations is being executed as desired. If you’re worried about this, you can force a specific order of operations using brackets (which we explore later in this lesson).


Exponents in Python are implemented with the double asterisk (**). As an example, 2 to the 4th power is calculated as follows:


#returns 16


The remainder function is a lesser-known mathematical function defined as the polynomial "left over" after dividing one polynomial by another. As an example, the remainder of 18 divided by 4 is 2, because 16 divides evenly into 4 and 18 minus 16 is 2.

Dealing with remainders can be difficult on paper but is very easy in Python. You can calculate remainders using the ‘%’ character. An example is below:


#returns 2


In Python, you can force your mathematical operations to execute in a certain order by using brackets. As an example, let’s say you had the following code:

2 + 3 * 20

#Returns 62

This code will first execute the 3*20 (giving 60) and then add 2, which gives 62. If you wanted the addition to be implemented prior to the division, you’d wrap it brackets like this:

(2 + 3) * 20

#returns 100

Note that round brackets, curly brackets, and square brackets are not equivalent in Python. This code would not execute in the same manner as the previous example:

[2 + 3] * 20

#WRONG - Don't Do This!

We’ll discuss how to properly use curly brackets and square brackets when we talk about data structures later in this course.

A Note on Whitespace

In programming, all of the spaces (and tabs) included in your programming are called ‘whitespace’. I wanted to pause the lesson for a moment to discuss how whitespace impacts your code.

The short answer is that whitespace doesn’t effect your code. To be specific, putting spaces between your math operations does not effect their meaning. A few examples:


#returns 16

2 ** 4

#also returns 16


#returns 4

2          +          2

#also returns 4

Variables in Python

In Python, we generally do not perform mathematical operations using numbers directly. We instead assign those numbers to variables and then manipulate the variables.

As an example, consider the following code:

a = 1

b = 2

a + b 

#returns 3

Variable Overwriting

Variable names are easily overwritten in Python (except in certain specific cases that we’ll discuss later). For example, if you executed the following code and printed the value in variable b, the value would be 4.

b = 6

b = 4

#b returns 4

The second variable assignment overwrites the first because it came later in the Python script.

Boolean Variables

So far in this lesson, we have only discussed numerical variables. There are many different types of data (called data structures) that can be assigned to variables outside of basic numbers.

We explore some of the more complicated data structures in their own lessons later in this course. However, in this lesson we will also take a moment to discuss a special type of variable called Boolean variables.

Boolean variables are a unique type of variable that can only have two values: True or False. You assign these variables like this:

trueBoolean = True
falseBoolean = False

These variables are useful in a number of cases - for example, evaluating whether to run certain blocks of code. We'll explore boolean variables in more detail later in this course.

Best Practices on Variable Naming

When creating variable names in Python, there are a few best practices that we should make sure to follow.

First, variable names cannot contain spaces. So you cannot name a variable ‘my name’. Instead, we use underscores - so the equivalent variable would be my_name.

Oftentimes, we don’t use underscores but instead practice a naming convention called “camel case” (sometimes stylized as camelCase). Camel case lists all of the word together without spaces, and capitalizes all of the first letters except the first word.

Here are a few examples of camel case variable names:





In this lesson, we discussed comments, operations, and variables in the Python programming language. These are the very foundations of Python - you should make sure to have a firm grasp on them before proceeding further through this course.