<< Chapter < Page Chapter >> Page >

The procedure for doing that is as follows:

  • Open the code visualizer .
  • Copy the example program code into the online text editor .
  • Select Python 3.3 in the pull-down list.
  • Click the button labeled Visualize Execution .
  • Use the Forward and Back buttons to step forward and backward through your code, one instruction at a time,while observing the positions of the red and green arrows and observing the information that appears on the screen to the right of the code window.

Discussion and sample code

The earlier module titled Itse1359-1060-Syntax in this book presented and explained the two Pythonprograms shown in Listing 1 and Listing 2 . I will illustrate the use of the code visualizer with this pair of sample programs.

Listing 1. A sample program with proper indentation.
A = 3 B = 4if B>A: print(A) # begin groupprint(B) print(A + B) # end groupA = 6 # not part of above group print(A)
Listing 2. Another sample program with proper indentation.
A = 4 B = 3if B>A: print(A) # begin groupprint(B) print(A + B) # end groupA = 6 # not part of above group print(A)

Open the online text editor

When you first open the online text editor , a portion of the screen will look like Figure 1 .

Figure 1. The online text editor.

missing image

The blank portion at the top of Figure 1 is the text editor portion of the screen.

Three drop-down boxes

There are three drop-down boxes at the bottom of Figure 1 that allow you to selectdifferent options. The different options in these boxes control the manner in which the output information is presented as youstep through the program. In some cases, you might want to step through the same program more than once with different sets of options selected.

Beginning the visualization process

Figure 2 shows the result of pasting the code from Listing 1 into the text editor and pressing the button in Figure 1 labeled Visualize Execution .

Figure 2. Beginning the visualization process.

missing image

The red and green arrows

As indicated by the key in the bottom left corner of Figure 2 , two arrows will appear next to the code as you step through the code. A redarrow shows the instruction that will be executed the next time you press the Forward button. (Pressing the Back button moves the red arrowback one step.) The green arrow shows the instruction that was most recently executed. (The green arrow isn't visible in Figure 2 because it is underneath the red arrow at the beginning.)

Output following three presses of the Forward button

Figure 3 shows the result of pressing the Forward button three times.

Figure 3. Output following three presses of the Forward button.

missing image

We see from the green arrow on the left that the relational test in the if statement was the most recently executed instruction.

We see on the right that the variables named A and B contain references (pointers) to objects of type int containing values of 3 and 4 respectively.

Because B is greater than A , the relational test in the if statement (pointed to by the green arrow) returned true when that statement was executed. This means that the threestatements in the indented block following the if statement will be executed. The red arrow points to the first statement in the indented blockmeaning that it will be executed the next time the user presses the Forward button.

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Itse 1359 introduction to scripting languages: python. OpenStax CNX. Jan 22, 2016 Download for free at https://legacy.cnx.org/content/col11713/1.32
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Itse 1359 introduction to scripting languages: python' conversation and receive update notifications?

Ask