Python Installation & Command Line Basics

1. Your Programming Toolkit: Python and a Code Editor

First, what is Python? Python is a popular, high-level programming language known for its clear and readable syntax. This makes it an excellent language for learning programming fundamentals and algorithmic concepts. The code you write is processed by a program called the Python interpreter, which translates your commands into instructions the computer can execute.

To write your Python code, you'll use a code editor. While you could use a basic text editor like Notepad, a proper code editor offers helpful features like syntax highlighting (coloring your code to make it more readable) and other tools that make programming much easier.

2. Setting Up Your Environment

Now, let's get Python and a code editor installed on your computer. We'll use the video below and a detailed article to guide you.

For more detailed, step-by-step instructions that you can read at your own pace, the following article from Real Python is an excellent resource. It covers installation for Windows, macOS, and Linux.

A Critical Step for Windows Users

If you are using Windows, it is very important that you check the box that says "Add python.exe to PATH" during installation. The PATH is a list of directories that your command line searches when you type a command. Adding Python to the PATH allows you to run the Python interpreter from any folder on your computer by simply typing python.

3. Verifying Your Installation with the REPL

Once the installation is complete, let's verify that everything is working. We'll do this using the command line and a feature called the Python REPL (Read-Eval-Print Loop). The REPL is an interactive shell where you can type Python code one line at a time and see the result immediately.

1. Open your command line:

   • Windows: Press the Win key, type PowerShell or cmd, and press Enter.
   • macOS/Linux: Open the Terminal application.

2. Check the Python version: Type the following command and press Enter. You should see the version number you just installed.

   python --version
   

   Note: Depending on your system (especially on macOS and Linux), you might need to use python3 instead of python. If the first command gives an error, try python3 --version.

3. Start the REPL: Now, type python (or python3) by itself and press Enter.
   You should see some information about the Python version followed by a >>> prompt. This prompt means you are now in the Python interactive session!

The article below explains the REPL in more detail.

To exit the Python REPL and return to your normal command line, you can type exit() and press Enter.

4. Writing and Running Your First Program

Now that Python is installed, let's write and run a complete program. The traditional first program is called "Hello, World!".

Step 1: Write the Code

Open the PyCharm editor you installed earlier.

1. Create a new project. The Mosh video (from 03:02 onwards) shows how to do this.
2. Inside your project, create a new file and name it hello.py. The .py extension is how we tell the computer that this is a Python file.
3. In the file, type the following single line of code:

print("Hello, World!")

This code uses the built-in print function to display the text string "Hello, World!" on the screen. Save the file.

Step 2: Run the Code from the Command Line

While you can run code directly inside PyCharm, a fundamental skill for any programmer is to run scripts from the command line.

1. Open your command line/terminal (PowerShell, cmd, or Terminal).

2. Navigate to the correct directory. You need to tell the command line where you saved your hello.py file. Use the cd (change directory) command. For example, if you saved the project on your Desktop in a folder called python_projects, you might type:

   cd Desktop/python_projects
   

3. Execute the script. Once you are in the same directory as your hello.py file, type the following command and press Enter:

   python hello.py
   

   (Remember to use python3 if needed for your system).

You should see the text Hello, World! printed in your terminal. Congratulations, you've just run your first Python program!

For a textual explanation of this process, refer to the following resource.

Conclusion

In this lesson, you have successfully set up your complete Python development environment. This is a huge and essential first step.

Here are the key takeaways:

• You installed the Python interpreter, the engine that runs your code.
• You installed PyCharm, a code editor that will help you write your programs.
• You learned how to verify your installation and experiment with code using the Python REPL.
• You wrote a simple "Hello, World!" program and, most importantly, learned how to run it from the command line.

You are now fully equipped to start programming. In our next lesson, we will begin exploring the building blocks of Python. We'll learn how to use variables to store information, work with basic data types like numbers and text, and write programs that can interact with a user.