Writing and Running Your First Python Program

From Idea to Working Program

Writing software is more than typing instructions. It is a structured journey from an idea to a working program that solves a problem. In this course, you will repeatedly move through a simple pattern: understand what you want to build, write a small piece of Python, run it, check the result, and then decide what to add next.

Starting small reduces risk. A simple version is easier to test, helps you discover whether your basic approach works, and gives you a stable foundation for later improvements. If the approach is wrong, you have invested less time before correcting it.

The Five Development Phases

The software development process has five phases. Each phase has a different purpose, and using them in order helps you plan work, find problems, and create software that can be used and refined.

For a small Python script, What might mean deciding the problem the script should solve. Do It means writing the script. Test means running it with test data and checking for errors. Use means applying it to real data to ensure it works. Maintain means refining the script based on what you learn.

The Do It-Test-Use Cycle

Although all five phases belong to the complete process, practical programming usually proceeds iteratively. You analyze and design a small part, implement it, test and debug it, use it to verify correctness, and then add a feature. The cycle repeats as the program grows.

Where Your Python Runs

Python is a programming language: a formal set of instructions that a computer can understand and execute. In this course, you write Python code in your browser, and the code runs in the cloud on a server. The server's Python interpreter reads and executes the code, then sends the result back to your browser.

Writing Versus Running

Writing code means entering a Python instruction or placing it in a script. Running code means sending that instruction to the Python environment so the interpreter can read and execute it. The two actions are connected, but they are not the same action.

In the REPL, the distinction happens quickly: you enter one line, run it, see the result, and then enter another line. In a script, you can write several lines first and run the complete saved file. Both modes use the same Python language; they differ in how code is organized and executed.

Your First Python Statement

A Python statement is a complete instruction. The simplest statement in this lesson is a call to the print function. The function displays the text supplied to it.

print("Hello, Python")

Hello, Python

Every function call follows the pattern function name, parentheses, and input inside the parentheses. In this statement, print is the function name. The parentheses show that the function is being called, and the text inside them is the argument given to the function. When the interpreter runs the statement, the text appears on the screen.

Names and Values

After printing a fixed message, you can give values names. A variable is a name that holds a value. Assignment uses the equals sign to associate a value with a variable name so that you can use the name later.

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

Alice
25

When you use a variable name, Python retrieves the value associated with that name. This makes code readable and reusable because you can use a name instead of repeatedly typing the same value.

Mistakes Beginners Make

• Treating writing code as the same as running code

  An instruction produces output only when the interpreter reads and executes it.

  Fix: After entering or saving the instruction, run it in the course environment.

• Trying to build every feature before testing

  Problems may be discovered late, after more time and complexity have been added.

  Fix: Build a simple version, test it thoroughly, use it, and then add the next feature.

• Confusing a function name with a function call

  Parentheses indicate that the function is being called and contain its input.

  Fix: Use the function name followed by parentheses with the argument inside.

• Expecting a variable name to display its value without an instruction

  Assignment associates a value with a name; print is the statement described for displaying a value.

  Fix: Use print with the variable name when you want the value displayed.

Practice the Full Process

What to Remember

1. The five software development phases are What, Do It, Test, Use, and Maintain.
2. The recommended iterative approach builds a simple version, tests it, uses it to verify correctness, and then adds features.
3. In this course, Python runs in a cloud-based interpreter through your browser, so no installation is needed.
4. The REPL runs Python one line at a time, while a script is a saved file containing multiple lines of code.
5. A print statement contains a function name, parentheses, and an argument; running it makes the argument appear as output.
6. Writing code and running code are different: writing creates the instruction, while running sends it to the interpreter for execution.