[title, rating]. Having worked with lists before, she feels confident and jumps straight into coding:
music_library = [
["Imagine", 5], # index 0
["Thriller", 4], # index 1
["Hey Jude", 5] # index 2
]
# Change "Thriller" rating from 4 to 3
music_library[1][1] = 3
print(music_library)
[['Imagine', 5], ['Thriller', 3], ['Hey Jude', 5]]. This works for now, but only because Audrey remembers that:music_library[1][1] are risky, Audrey tries to make her code more flexible with helper functions:
def find_song_index(library, song_title):
for i in range(len(library)):
if library[i][0] == song_title: # Title is at index 0
return i
def update_rating(library, song_title, new_rating):
idx = find_song_index(library, song_title)
library[idx][1] = new_rating # Still assumes rating is at index 1
music_library = [
["Imagine", 5],
["Thriller", 4],
["Hey Jude", 5]
]
update_rating(music_library, "Thriller", 1)
print(music_library)
music_library = [
["Imagine", 5, 120], # Now includes play count
["Thriller", 4, 230],
["Hey Jude", 5, 150]
]
update_rating function still uses index 1 for ratings, which still works... for now[title, play_count, rating], the function will corrupt datasong[2] the rating or the play count? Could it become genre if we shift the order next week?weight in pounds or kilograms? Are dates in MM/DD/YYYY or DD/MM/YYYY format?Point class, or a “student record” type, or a database schema. You simply followed it. But now, you’re the one deciding how to store data. Failing to define it clearly is a recipe for frustration.
title, rating, play_count).ASongis a Python list of the form[title, rating, play_count], where:
titleis a string (e.g.,"Imagine").ratingis an integer in[1..5].play_countis a nonnegative integer (0 or greater).
artist,” she’ll update the definition to: [title, rating, play_count, artist]. Every function that touches Song refers back to this “blueprint,” instead of guessing how many fields there are or which index is which.
rating can’t exceed 5. In Python, you might or might not write code to check that. But if you do—say, with an if new_rating & 5 check—then you can detect bad data early. In other languages, like Java, you could have a method that rejects any rating above 5 automatically. Either way, once you’ve written down “rating is 1–5,” it’s easier to test or enforce that assumption.
play_count can’t exceed 9999, how would you reflect that in your definition? Could you detect an invalid play_count in code and raise an error or log a warning?
public class Song {
// 'private' means these variables can only be changed
// using the methods we provide below
private String title; // The song's name
private int rating; // Must be 1-5
private int playCount; // Must be >= 0
// Methods to safely change the rating
public void setRating(int newRating) {
if (newRating < 1 || newRating > 5) {
throw new IllegalArgumentException("Rating must be 1-5");
}
rating = newRating;
}
// Methods to safely change the play count
public void setPlayCount(int newCount) {
if (newCount < 0) {
throw new IllegalArgumentException("Play count can't be negative");
}
playCount = newCount;
}
// Method to safely change the title
public void setTitle(String newTitle) {`
if (newTitle == null || newTitle.isEmpty()) {
throw new IllegalArgumentException("Title cannot be empty");
}
title = newTitle;
}
}
private, meaning they can only be changed using our special methods.Song song = new Song();
// These won't compile - Java catches type mismatches
song.setRating("five"); // Error: rating must be a number!
song.setPlayCount("lots"); // Error: play count must be a number!
// These compile but fail when run - our methods catch invalid values
song.setRating(10); // Error: rating must be 1-5
song.setPlayCount(-5); // Error: can't have negative plays
song.setTitle(""); // Error: title can't be empty
[title, rating, play_count]— serves as a stable reference point: any code that modifies or reads a field can check the blueprint to avoid silent breakage.
play_count less than 0). By combining these steps— data definition, then function contracts, then testing—we build a robust, iterative path to maintainable code.
library[0][1] to change a song’s rating. Which of the following is the best explanation of why this is risky?[0][1] out of range.rating to [2], code referencing [1] corrupts data.[title, rating, play_count]) before writing code?True.
False.
[title, author, pages])pages >= 1, or title non-empty)title is a non-empty string (e.g. "Pride and Prejudice").author is a non-empty string (e.g. "Jane Austen").page_count is an integer >= 1.genre and publication_year. The crucial idea is documenting each field and its valid range or type.
