Special Ways to Execute Python in this Book¶

This book provides two additional ways to execute Python programs. Both techniques are designed to assist you as you learn the Python programming language. They will help you increase your understanding of how Python programs work.

First, you can write, modify, and execute programs using a unique activecode interpreter that allows you to execute Python code right in the text itself (right from the web browser). Although this is certainly not the way real programs are written, it provides an excellent environment for learning a programming language like Python since you can experiment with the language as you are reading.

Take a look at the activecode interpreter in action. If we use the Python code from the previous example and make it active, you will see that it can be executed directly by pressing the run button. Try pressing the run button below.

Now try modifying the activecode program shown above. First, modify the string in the first print statement by changing the word adds to the word multiplies. Now press run. You can see that the result of the program has changed. However, it still prints “5” as the answer. Modify the second print statement by changing the addition symbol, the “+”, to the multiplication symbol, “*”. Press run to see the new results.

If you are logged in, you can also make changes and save them for reloading later. Save and Load allow you to keep one copy of the program you are working on. For example, press the Save button now. You have just saved the current contents of the activecode window. Now make a few changes and press the Run button. You have changed the current program. Press Load to return your program to its previously saved state.

In addition to activecode, you can also execute Python code with the assistance of a unique visualization tool. This tool, known as codelens, allows you to control the step by step execution of a program. It also lets you see the values of all variables as they are created and modified. In activecode, the source code executes from beginning to end and you can see the final result. In codelens you can see and control the step by step progress. Note that the red arrow always points to the next line of code that is going to be executed. The light green arrow points to the line that was just executed. Click on the “Show in Codelens” button to make the codelens window show up, and then click on the Forward button a few times to step through the execution.

Sometimes, we will present code examples explicitly in a codelens window, as below. When we do, think of it as an encouragement to use the codelens features to step through the execution of the program.

Check your understanding