Module Import Flow

Run the Module Import Flow MicroSim Fullscreen

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

<iframe src="https://dmccreary.github.io/stem-robots/sims/module-import-flow/main.html"
        height="502px"
        width="100%"
        scrolling="no"></iframe>

About This MicroSim

Every .py file on your robot is a module, which is a file of code that other files can use. The import statement links one module to another. This MicroSim shows three files from the chapter:

• config.py (blue) holds the pin numbers as UPPERCASE constants, such as RIGHT_FORWARD_PIN = 11.
• motors.py (green) runs import config and uses config.RIGHT_FORWARD_PIN to set up the motor pin.
• main.py (orange) runs import config and import motors, prints the pin, and calls motors.stop_all().

Arrows show which file imports which. Every spot that reads config.RIGHT_FORWARD_PIN is highlighted in yellow, with an orange badge that shows its current value. The small wiring picture on the left shows which GP pin the right forward motor wire is plugged into.

When you change the pin in config.py, every highlighted spot follows along at once. You edit 1 line. Turn on Hard-code pins instead and the same number is typed by hand in 5 places. Now changing config.py does nothing. The code still drives GP11, and the wiring picture shows the motor as not connected.

How to Use

1. Press Run main.py. The console prints the import order one step at a time, and each import arrow pulses gold as it runs. Notice that config.py loads only once, even though two files import it.
2. Change RIGHT_FORWARD_PIN to 13. Watch the badges in motors.py and main.py change, and the orange wire move to GP13.
3. Check Hard-code pins instead (no config.py). Change the pin again and read the Pin mismatch message and the Lines to edit counter.
4. Press Reset to return to pin 11 with the config.py pattern.

This MicroSim goes with the modular programming section of Chapter 5: Data Structures, Modular Programming, and Version Control.

Lesson Plan

Grade Level

Grades 8–12 (introductory programming with a physical robot)

Duration

15 minutes

Prerequisites

• Importing built-in modules with import time and from time import sleep (Chapter 4: Control Flow, Functions, and Exception Handling)
• Defining and calling functions (Chapter 4)
• Variables and constants (Chapter 3: MicroPython and Development Environment Setup)

Learning Objective

Students will be able to explain (Bloom's Taxonomy: Understand) how import links files together, and predict which files change behavior when one value in config.py changes.

Activities

1. Trace the imports (4 min). Students press Run main.py and write down the order of the console lines. Ask why config.py loads only once.
2. Predict the change (3 min). Before changing the pin to 13, students list every place in the three files that will show 13 afterward. They check their list against the yellow badges.
3. Break the pattern (4 min). With Hard-code pins instead on, students change the pin to 13 and count the stale numbers. They explain, in two sentences, why the motor would not move on the real robot.
4. Connect to the kits (4 min). Students open a config.py from one of the robot kits and find two other constants that other files import.

Assessment

• Challenge: You move the right forward motor wire from pin 11 to pin 13. How many lines must you edit with the config.py pattern, and how many with hard-coded pins? Answer: 1 line with config.py, 5 lines when hard-coded. Students check the Lines to edit counter.
• Exit ticket: "A teammate changes a pin number in motors.py instead of config.py. What problem might this cause later?"
• Rubric (4-point): Exemplary explains that importing shares one definition across files, predicts every file affected by a change, and connects the pattern to separation of concerns. Proficient explains the import link and predicts the affected files. Developing knows config.py holds pins but cannot explain how other files see the change. Beginning believes each file needs its own copy of the pin numbers.

References

1. Chapter 5: Data Structures, Modular Programming, and Version Control - the config.py pattern and the motors.py module example.
2. Python Tutorial: Modules - official explanation of modules and the import statement.
3. MicroPython machine.Pin - the Pin class used to set up the motor pin.
4. Separation of concerns (Wikipedia) - the design idea behind keeping hardware settings in one file.
5. Magic number (programming) (Wikipedia) - why unexplained numbers typed in many places cause bugs.