Your First Python Program

A Language Built for Both Learning and Work

Python is a programming language: a formal set of instructions that a computer can understand and execute. What makes Python especially approachable is its balance. It prioritizes readability and simplicity without giving up the power needed for useful programming tasks.

Python combines three important characteristics. Its performance helps programs do useful work in reasonable time. Its extensive features, including a large standard library of pre-written code for common tasks, give programmers tools for diverse problems. Its clear syntax makes it easier to learn and express ideas. Together, these characteristics reduce the amount of boilerplate code you need to write while keeping the language capable enough for sophisticated applications.

From Browser to Python Output

This course runs Python code in your browser using a cloud-based interpreter. Your code does not run directly on your computer. When you write a line of code and press Run, the code is sent to a server, the Python interpreter on that server reads and executes it, and the result is sent back to your browser.

Writing Versus Running Code

Writing code means creating instructions in a form the Python interpreter can understand. Running code means asking the interpreter to read and execute those instructions. A line can exist in the editor without having produced any output yet; execution begins when you run it.

Your First Print Statement

A Python statement is a complete instruction. The simplest statement in this lesson is a call to the print function. The print function displays what you give it on the screen.

print("Hello, Python")

The word print is the function name. A function is a reusable instruction. The parentheses indicate that you are calling the function, rather than merely mentioning its name. The text inside the parentheses is the input, called an argument. When Python executes this call, it displays the text Hello, Python.

Hello, Python

What Happens During Execution

Two Ways to Run Python

Python code can run line by line in the REPL or as a complete script file. The REPL is useful for experimenting and testing small ideas quickly. A script is a saved file containing multiple lines of Python code that you run as a complete unit.

Names and Stored Values

After a print statement, an important next idea is assignment. A variable is a name that holds a value. The equals sign assigns a value to a variable name so Python can remember it and allow you to use the name later.

name = "Alice"
age = 25
print(name)
print(age)

Alice
25

In the first line, the text Alice is assigned to the variable name. In the second line, the number 25 is assigned to age. When Python reaches print(name), it looks up the value associated with name and displays it. The same process happens for age. Assignment lets you use a readable name instead of repeatedly typing the same value.

Mistakes Beginners Make

• Expecting output immediately after writing code

  Writing places the instruction in the editor; it does not execute the instruction.

  Fix: Run the statement, then inspect the output returned by the course environment.

• Leaving out the parentheses in a function call

  A function call follows the pattern of a function name followed by parentheses containing its arguments.

  Fix: Write print("Hello, Python") with the argument inside parentheses.

• Thinking the code runs on your own computer

  The course sends your code to a cloud-based interpreter on a server.

  Fix: Use the browser environment provided by the course; no installation is needed for these lessons.

• Treating the REPL and a script as different languages

  The REPL and script files use the same Python language.

  Fix: Remember that the difference is how code is organized and executed: line by line in the REPL or as a complete file in a script.

Your First Practice Run

The Foundation for Later Programs

You have now followed the basic path of a Python program: write an instruction, run it through the interpreter, and inspect the output. You also saw the structure of a function call and learned that variables give names to values. These ideas will reappear in longer scripts and more advanced programs.

• Python combines performance, extensive features, and ease of use.
• Readable syntax and a large standard library reduce the amount of boilerplate code you need to write.
• This course runs Python in the cloud through a browser-based environment, so installation is not required.
• The REPL runs code line by line, while a script runs a saved collection of lines as a complete file.
• A print call uses a function name, parentheses, and an argument to display output.
• Assignment connects a variable name with a value that Python can retrieve later.