How to Save Your ROS 2 Project on GitHub

In this tutorial, I will show you how to store your ROS 2 project in a repository on GitHub.

Follow along with me click by click, keystroke by keystroke.

In case you’re not familiar with GitHub, GitHub is an online platform specifically designed for software development. It offers several key functionalities:

Version control: This allows you to track changes made to code over time. Think of it like a time machine for your code, letting you revert to previous versions if necessary.
Code storage: GitHub acts as a secure and centralized location to store and manage code projects. Think of it like cloud storage specifically for your code.
Collaboration: Teams can work together on projects by sharing code, discussing changes, and merging different contributions seamlessly.
Open-source contribution: GitHub is a hub for open-source projects, where developers can publicly share their code, contribute to existing projects, and learn from others.

Prerequisites

You have created a ROS 2 package inside a workspace.
I have created a ROS 2 workspace that is at this path /home/ubuntu/ros2_ws/.

My package is called ros2_fundamentals_examples and is at this path: /home/ubuntu/ros2_ws/src/ros2_fundamentals_examples/

You can see the complete repository here on GitHub.

Install Git

The first thing you need to do is install Git. Open a new terminal window, and type:

sudo apt-get update

sudo apt-get install git -y

Check the git version you have.

git --version

Configure Git

Configure your git username and email.

git config --global user.name "John Doe"

git config --global user.email "johndoe@example.com"

git config --global init.defaultBranch main

Initialize Git

Move to inside your project folder.

cd  ~/ros2_ws/src/ros2_fundamentals_examples/

Initialize the folder as a Git repository by running:

git init

This command allows you to start tracking changes to the files within that directory.

Add and Commit the Files to Your Local Repository

Add the files in your folder to the repository with the following command:

git add .

Commit your staged files to your local repository with:

git commit -m "Initial commit"

Create the Remote Repository on GitHub

Go to GitHub and log in.

Click on the “+” icon in the upper right corner and select “New repository.”

Name your repository.

Add a description (optional).

Choose whether the repository will be public or private.

Ignore the rest of the options.

Click “Create repository.”

Link the Local Repository to the Remote Repository

After creating your repository on GitHub, you’ll get a URL for that repository that looks like this: “https://github.com/…./ros2_fundamentals.git”

Go back to a terminal window, and link your local repository to GitHub with this command:

cd  ~/ros2_ws/src/ros2_fundamentals_examples/

git remote add origin <repository-URL>

Now log in to your GitHub account again.

Creating a Fine-Grained Personal Access Token

A personal access token is like a special key that lets you access your GitHub account from other apps or scripts. It’s more secure than using your password because you can control what the token is allowed to do.

Here are the official steps, but we will walk through everything together now.

First, verify your email address, if it hasn’t been verified yet.

In the top-right corner of the GitHub page, click on your profile picture.

From the menu, click “Settings.”

In the left sidebar of the settings page, scroll down until you see “Developer settings.”

Click on “Developer settings.”

In the left sidebar, under Personal access tokens, click Fine-grained tokens.

Click Generate new token.

Follow the steps to authenticate your identity on GitHub.

Under Token name, enter a name for the token.

Under Resource owner, select a resource owner. The token will only be able to access resources owned by the selected resource owner.

Under Expiration, select an expiration for the token.

Optionally, under Description, add a note to describe the purpose of the token.

Under Repository access, select which repositories you want the token to access.

If you selected Only select repositories in the previous step, under the Selected repositories dropdown, select the repositories that you want the token to access. I will select the ros2_fundamentals_examples repository.

Under Permissions, select which permissions to grant the token. Depending on which resource owner and which repository access you specified, there are repository and account permissions. You should choose the minimal permissions necessary for your needs.

I will grant “Read and write” permissions to all of the resources. If “Read and write” is not available for a particular resource, select “Read-only”.

Click Generate token.

Copy the personal access token that you see, and save it somewhere safe.

Push Code to GitHub

Finally, push your code from your local repository (the folder on your computer) to GitHub (the remote folder) with:

cd  ~/ros2_ws/src/ros2_fundamentals_examples/

git push -u origin main

Enter your GitHub Username.

Then, when it asks for your password, enter the personal access token you created in the previous section.

With this command we have created a two-way connection between your local code and GitHub.

The git push -u origin main command uploads your local code to GitHub while simultaneously setting up a tracking relationship between your local and remote branches.

The -u (or –set-upstream) flag tells Git to remember this connection, so in the future you can simply use git push or git pull without needing to specify where to push to or pull from.

origin refers to your GitHub repository, and main is the name of your branch.

Now if you go back to GitHub, you can see your repository.

Git Command Overview

When you make changes to your code on your computer, and want to get these code changes saved to GitHub, here is how you do it:

git add .

This command picks up all your new code changes and gets them ready to be saved. It’s like gathering up all your files into a neat pile.

git commit -m "description of changes"

This command saves these changes on your computer with a message explaining what you did. It’s like putting that pile of files into a labeled folder.

git push

This command sends all your saved changes to GitHub. Think of it like uploading your folder to the cloud so others can see it and you have a backup.

You’ll repeat these three steps each time you want to update your code on GitHub.

And if you’re working with other people, you should always download their changes first using git fetch, git status, and then git pull (one command right after the other) before you start working.

git fetch checks GitHub to see what changes exist – it’s like looking at a list of updates available but not downloading them yet. It tells you what’s different between your code and GitHub’s code.

git status shows you exactly what’s different between your local code and the code on GitHub after you’ve fetched. It’s like comparing your version with GitHub’s version to see what’s changed.

git pull actually downloads those changes from GitHub to your computer, bringing your local code up to date. It’s like clicking “download” on those updates you found with fetch and status.

These three commands help you safely check for and get any updates before you start working, which helps avoid conflicts with other people’s code changes.

Remove the Need to Use a Username and Password

If you want to not have to use a username and password every time you run “git push”, you can use SSH keys. This page has the official instructions on how to do that.

Here is the process…

Generate an SSH key pair (if you don’t already have one) by running:

ssh-keygen -t ed25519 -C "your_email@example.com"

When you get prompted for a password or saving location, just keep pressing Enter, which will accept the default.

Start the ssh-agent in the background.

eval "$(ssh-agent -s)"

Add your SSH private key to the ssh-agent:

ssh-add ~/.ssh/id_ed25519

Add the SSH public key to your Git server.

cat ~/.ssh/id_ed25519.pub

Copy the entire result to your clipboard by highlighting everything and copying it.

Go to your GitHub account “Settings” by clicking your profile icon in the upper right of the website.

Look for “SSH and GPG keys”.

Add a New SSH key.

Paste the copied key as an “Authentication Key”. Also add a title (you can make it whatever you want).

Click Add SSH key.

Go back to the main page of your repository on GitHub.

Find the SSH URL by clicking the green button labeled “Code”.

Copy the SSH URL that is in there.

Switch your repository’s remote URL to SSH by going to your Ubuntu Linux terminal window, and moving to the directory of your repository.

cd <path to your your local repository>

For example:

cd  ~/ros2_ws/src/ros2_fundamentals_examples/

git remote set-url origin git@github.com:username/repository.git

To confirm everything is setup properly, type:

git pull

If you get asked about the authenticity of the host, just type yes and press Enter.

That’s it.

Using SSH keys is a more secure and convenient method for machines where you regularly push changes, as it doesn’t require entering your credentials after the initial setup.

Keep building!

How to Create Basic Programs Using Python

In this tutorial, we are going to build basic programs using Python.

Prerequisites

You have completed this tutorial.
I am using VS Code for my Python development environment, but you are free to use any development environment you wish.

Build a Basic Calculator

Let’s start by building a basic calculator. This exercise will help you understand how to handle user input and perform basic arithmetic operations in Python.

Open a new terminal window, and move to the directory where we will store our code.

cd ~/Documents/python_tutorial

I will open VS Code.

code .

Right-click in the Explorer pane and select “New File”.

Name the file basic_calculator.py, and press Enter.

First, let’s ask the user to input two numbers. Type the following lines:

num1 = float(input("Enter first number: "))
num2 = float(input("Enter second number: "))

These commands prompt the user for input, converting the input into floating point numbers for arithmetic operations.

Next, we need to ask the user to choose the operation. Add this line:

operation = input("Choose the operation (+, -, *, /): ")

Now, we’ll use conditional statements to perform the operation selected by the user.

if operation == '+':
    result = num1 + num2
elif operation == '-':
    result = num1 - num2
elif operation == '*':
    result = num1 * num2
elif operation == '/':
    if num2 != 0:
        result = num1 / num2
    else:
        result = "Error! Division by zero."
else:
    result = "Invalid operation selected."

print(result)

This if-else structure helps our calculator decide what to do based on the user’s choice.

After writing the code, save your file. Let’s now run our program to see how it works.

Enter the numbers and the operation when prompted.

Watch as your program calculates and displays the result.

Making Your Program Executable

Let’s see how to make basic_calculator.py executable. We will do this directly from the command line. This will enhance your workflow by allowing you to run your Python scripts without explicitly calling the Python interpreter each time.

Let’s begin by opening the basic_calculator.py script we created in the previous lecture. Once open, we need to add a shebang line at the very top of the file.

Type the following line as the first line in your file:

#!/usr/bin/env python3

This shebang line tells the system that this script should be run using Python 3, which we’ve installed on our machine. Make sure this line is at the top, before any other code.

After adding the shebang, save your file.

The next step is to make the script executable. We’ll do this using the terminal.

Open your terminal in Visual Studio Code by going to View -> Terminal.

Navigate to the directory where your basic_calculator.py file is located. Now, type the following command:

cd ~/Documents/python_tutorial

chmod +x basic_calculator.py

This command changes the file’s permissions, making it executable.

Now, you can run your Python script directly from the command line.

To run your script, simply type the following in your terminal:”

./basic_calculator.py

Notice how we didn’t have to type ‘python3’ before our script name. The system recognizes it as an executable file and runs it using the Python interpreter specified in the shebang line.

Go ahead and test different inputs to see how your calculator works now as an executable script.

Doing Basic Calculations

Let’s explore how to perform basic calculations in Python. We’ll cover addition, subtraction, multiplication, division, and a bit about modulus operations.

Let’s get started by opening your code editor. We’ll create a new file named basic_calculations.py.

In this file, we’ll write small code snippets to demonstrate each type of calculation. First, let’s start with addition.

# Addition
print("Addition of 5 + 3 is:", 5 + 3)

This will output the sum of 5 and 3. Now, let’s do subtraction.

# Subtraction
print("Subtraction of 5 - 3 is:", 5 - 3)

Next, we have multiplication.

# Multiplication
print("Multiplication of 5 * 3 is:", 5 * 3)

And then division.

# Division
print("Division of 5 / 3 is:", 5 / 3)

Division in Python gives you a float. If you need the integer quotient, you can use the floor division operator.

# Floor Division
print("Floor division of 5 // 3 is:", 5 // 3)

Lastly, let’s look at the modulus operation, which gives the remainder of a division.

# Modulus
print("Modulus of 5 % 3 is:", 5 % 3)

After typing these examples, save your file. Now, let’s run this script to see the output of these basic calculations.

You should see the results for each operation displayed in the terminal. These operations are fundamental to programming and form the basis for more complex algorithms.

Working with Random Values

Let’s learn how to work with random values in Python. This capability is essential for simulating uncertainty in robotics applications and for creating varied testing scenarios.

Let’s start by opening your code editor. We’ll create a new file and name it working_with_random.py.

To generate random numbers, Python provides a module named random. First, we need to import this module.

import random

Let’s begin with generating a random integer. We’ll use the randint function, which returns an integer between the specified range.

# Generate a random integer between 1 and 10
random_integer = random.randint(1, 10)
print("Random integer between 1 and 10:", random_integer)

Next, we’ll generate a random float. The random function returns a floating-point number between 0.0 and 1.0.

# Generate a random float
random_float = random.random()
print("Random float between 0.0 and 1.0:", random_float)

Sometimes, you may want to generate a float within a different range. You can do this by multiplying the result of random().

# Generate a random float between 0.0 and 5.0
random_float_in_range = random.random() * 5
print("Random float between 0.0 and 5.0:", random_float_in_range)

We can also pick a random element from a list. Let’s create a list of colors and select one randomly.

# Pick a random element from a list
colors = ['red', 'blue', 'green', 'yellow']
random_color = random.choice(colors)
print("Random color selected:", random_color)

Lastly, if you want to shuffle the items in a list randomly, you can use the shuffle method.

# Shuffle a list
random.shuffle(colors)
print("Shuffled colors:", colors)

After entering these examples, don’t forget to save your file. Now, let’s run the script to see how random values are generated.

You’ll see the outputs for each of the random operations we scripted. This functionality is invaluable for creating diverse and dynamic environments in simulations and tests.

Using Nan and Infinity

Let’s explore how to work with NaN (Not a Number) and Infinity in Python. These are special floating-point values that you may encounter in numerical computations, especially when dealing with undefined or unbounded values.

Let’s start by opening your code editor. We’ll create a new file and name it nan_and_infinity.py.

To use NaN and Infinity, Python doesn’t require any special imports as they are part of the standard float type. Let’s start with Infinity.

# Positive Infinity
positive_infinity = float('inf')
print("Positive Infinity:", positive_infinity)

# Negative Infinity
negative_infinity = float('-inf')
print("Negative Infinity:", negative_infinity)

These lines create variables for positive and negative infinity. Operations with these values yield predictable results, following rules of mathematical infinity.

Next, we have NaN. It’s a special value used to denote that a result of a computation cannot be defined in meaningful terms.

# NaN example
not_a_number = float('nan')
print("Example of NaN:", not_a_number)

Let’s see some operations with NaN. Any operation involving NaN typically results in NaN, indicating an invalid result.

# Operations with NaN
print("NaN added to a number:", not_a_number + 5)
print("NaN multiplied by a number:", not_a_number * 2)

Interestingly, comparing NaN with anything, even itself, is always false. This is useful for checking if a value is NaN.

# Checking if a value is NaN
print("Is NaN equal to NaN?:", not_a_number == not_a_number)

To properly check for NaN, we use the math.isnan() function from the math module.

import math
print("Using math.isnan() to check NaN:", math.isnan(not_a_number))

Now, let’s run the script to see how NaN and Infinity behave in Python.

You’ll see the outputs for each operation, illustrating how special floating-point values like NaN and Infinity are handled in Python.

That’s it. You have gotten some good experience building programs in Python to perform fundamental calculations.

Thank you, and I’ll see you in the next tutorial.

Keep building!

How to Install Python in Ubuntu Linux – ROS 2

In this tutorial, we’re going to walk through how to install Python on Ubuntu Linux. Whether you’re setting up your development environment for the first time or updating to the latest version, this tutorial will ensure you get Python installed correctly on your system.

Prerequisites

You have a computer that is running Ubuntu (I’m running Ubuntu Linux inside a virtual machine on Windows).
You have installed ROS 2.
You have installed and configured Visual Studio Code for ROS 2 (Optional)

I am going to start by creating a file for all the code I will write in this tutorial.

Open a terminal window.

Type the following commands:

mkdir -p ~/Documents/python_tutorial

cd ~/Documents/python_tutorial

Let’s start by checking which version of Python we have installed.

python3 --version

Press Enter.

This command will tell you the version of Python 3 that is currently installed.

If Python 3 is not installed or if you need a different version, we can install it using Ubuntu’s package manager.

sudo apt-get update

sudo apt-get install python3

If you also need pip, which is the Python package installer, you can install it by typing:

sudo apt install python3-pip

After the installation has completed, you can verify that Python and pip are installed correctly by repeating the version check for Python and also checking pip by typing:

pip3 --version

That’s it. You now have Python and pip installed on your Ubuntu system. With Python set up, you’re ready to start developing applications, including those for robotics projects.

Thanks, and I’ll see you in the next tutorial.