sp24-lab12

Materials for week 12 lab in CS-370, which includes Ch. 23 "A File Viewer" adapted from Software Design by Example by Greg Wilson.

April 23, 2024

Organization:

• SDX-ch23: The code files for the SDX Ch. 23 activity (as downloaded directly from the book website, unmodified)

Team Members for Part 1

Molly and Jas

Team Roles for Part 1

Who will start out as

• DRIVER: Molly
• NAVIGATOR: Jas

You will switch halfway through this activity.

Part 1 Documentation

Write your answers to the questions below.

• What were the main ideas from SDX chapter 23? Using the curses modules and handling interactions of different parts of a system (screen size, key board input).

• What questions did you have about the material in the chapters? What did you find confusing? We both found the section on refactoring to be a little confusing.

Exercise 0: Run the code

Let's start by running the 6 final versions of the code from the conclusions of sections 1, 2, 3, 4, 5, and 6.

As you go along, review the code you are running and address the questions in the exercises.

Section 1: Curses

Run python3 show_lines.py 5 logfile

Verify that you see white text on a black screen. Typing q should quit the program.

Try increasing the number of lines to 10 and verify you see ten lines of text.

Then increasing the number of lines to 50 and verify the program crashes as described.

• Why does open_log need the line global LOG? What happens if it is removed? Modify global variable otherwise it will modify the local variable it creates.
• Why doesn’t the log function need this statement? We want it to edit the global version of log, and it's passed a copy of the variable.

Section 2: Windowing

Run python3 cursor_const.py 5 logfile python3 cursor_const.py 50 logfile

• This version should not crash. But can you see 50 lines of text? Why or why not? We cannot see 50 lines of text since the window size isn't set up correctly.

Section 3: Moving

Run python3 move_cursor.py 10 logfile

Verify that there is a cursor that moves along with the arrow keys, and you can move the cursor outside the bounds of the displayed text. If you move the cursor outside the window, the viewer will crash.

Section 4: Refactoring

Run python3 buffer_class.py 10 logfile and verify that it behaves exactly like the previous version

• as it should, since it is only a refactoring.

• What are all the classes defined in this version of the file viewer application? Buffer and BufferApp

• What are the factory methods? make_window(), make_buffer(), make_cursor()

• Why do you think the author paused here to refactor before fixing the bugs in the previous version of the code? We have classes that are doing too many things. For example, there is too much responsibility in main since it does stuff with window, move, curser. and key inputs. We want to refactor before implementing other things.

Section 5: Clipping

Run python3 clip_fixed.py 10 logfile Verify that the cursor does not move outside the bounds of the text.

• However, there is another bug. What is it? (If necessary, use CTRL-C to interrupt the program.) I can scroll outside the dower bound of the text
• What are all the classes defined in this version of the file viewer application? ClipCursorFixed, ClipAppFixed

Section 6: Viewport

Run python3 viewport.py 50 logfile Verify that you can scroll vertically through the text.

• What are all the classes defined in this version of the file viewer application? ViewportCursor, ViewportBuffer, ViewportApp
• Taking the file viewer application as a whole, do you find the code easy or difficult to read and understand? Why or why not? You might consider Ousterhout's idea of "classitis." I found it harder to read and understand because of "classitis". Had to traceback classes and would lose my spot.

Exercise 1: Quitting the application

In the file dispatch_keys.py, add a method to the DispatchApp class so that once again you can type q to quit the application.

Exercise 2: Horizontal scrolling

Modify the application to scroll horizontally as well as vertically.

Rather than creating yet another version of the app with yet more child classes, you can modify the code in viewport.py

Exercise 3: Line numbers

Modify the file viewer to show line numbers on the left side of the text. The line numbers should not move when scrolling horizontally.