Day 16

For next time

• Project Toolbox 3 due Thursday, March 28
• MP4 is now due on Tuesday, April 2 (see Canvas announcement)
• Friday class will be devoted to starting the Final Team Project (not MP4). Be sure to attend (and let us know in advance if you can’t).
• Think Python Chapter 19 “The Goodies” is the assigned reading for next time, but there is no required Reading Journal. This chapter has lots of fun and useful material for you to explore on your own.

Organizing large projects

As projects grow in scope and complexity, organization becomes more important. Fortunately, Python makes it fairly easy to add structure as you go.

Interactive

>>> print("Hello, SoftDes!")

In Python it’s quick and easy to get started and test your ideas interactively in the shell. Unfortunately these explorations are ephemeral, and it’s difficult to make changes and run the program again, so we quickly move beyond this stage.

Script

Your first Python script may be simply code from an interactive session pasted into a .py file so that you can edit and re-run it (as well as share it with team mates). This type of code is often linear (lacking reusable functions) and disorganized (a first draft).

Program

We consider a Python program to be a more evolved version of a script, with defined functions, classes, documentation, etc.

Modules

As your program gets bigger, grows beyond what can comfortably fit in one file. To create a module in Python, you simply write a .py file as always. Code in the module can then be imported from other modules using the filename (minus .py).

As a side-note, this is why we typically put all code to be run inside an if __name__ == "__main__": ... block at the bottom of the file. This way it will be run if the module is run by itself, but not if it is imported by another program.

Packages

For really big projects, you may even grow beyond a single directory. Python allows you to organize your modules into directories and refer to them as packages. All you need to do is place a (possibly empty) file called __init__.py in the folder along with your Python module files. Note: Your code for this class may never get quite this big and that’s ok. From a style perspective I would consider this going a bit too far with organization for the BrickBreaker example shown.

Read about Python modules for all the details.

We’ve added some more organization to the BrickBreaker example repository showing how a project might gradually evolve through these steps. Browse through the git history to see the changes over time.

Exercise:

Think about and sketch out how you would reorganize your project code into modules that group related code.

As a caveat, this type of major refactoring can create lots of merge conflicts if you are not careful. It is best to make sure everything is checked in first, do the exercise together as a team, and have test cases before and after the restructuring to make sure nothing breaks. Now might not be the right time to do the actual reorganization, and that’s OK.