def update_rating(library, song_title, new_rating):
for entry in library:
if entry[0] == song_title:
entry[1] = new_rating
return
# Mai's attempt
songs = [["Hey Jude", 4, 10]]
result = update_rating(songs, "Hey Jude", 5)
print(f"Update succeeded: {result}") # Prints: Update succeeded: None
# Later...
update_rating(None, "Hey Jude", 5) # Crashes!
update_rating(songs, "Hey Jude", 10) # Sets rating to 10 (invalid!)
update_rating([], "", -1) # Silently does nothing
Mai: "Let me write down what confused me when I tried using your function..."Mai writes on a napkin:
update_rating needs:
def update_rating(library, song_title, new_rating):
"""
Updates a song's rating. The song must exist in the library.
We require:
- library is a non-None, non-empty list of songs
- song_title is a non-empty string
- new_rating is an int between 1 and 5
Returns True if found and updated, False if song not found.
Raises ValueError for invalid inputs.
"""
if library is None or len(library) == 0:
raise ValueError("Library cannot be None or empty")
if not song_title: # Catches empty strings
raise ValueError("Song title cannot be empty")
if not (1 <= new_rating <= 5):
raise ValueError("Rating must be 1-5")
# ... rest of implementation ...
def find_favorite_songs(library):
"""What would you write here?"""
result = []
for song in library:
if song[1] >= 4:
result.append(song[0])
return result
Mai: "Look what I found! We can actually tell Python what types our function expects:"def update_rating(library: list, song_title: str, new_rating: int) -> bool:Audrey: "That’s cool! So anyone can see that new_rating must be an integer?"Mai: "Exactly! And the -> bool means it returns True or False."
def update_rating(library: list, song_title: str, new_rating: int) -> bool:
"""
Updates the rating for a song in the music library.
Args:
library: A list of songs, each [title, rating, play_count].
Cannot be None or empty.
song_title: The title to search for. Must be non-empty.
new_rating: New rating value, must be in range [1..5].
Returns:
True if the song was found and updated, False otherwise.
Raises:
ValueError: If any inputs violate their constraints.
Example:
>>> songs = [["Hey Jude", 3, 10]]
>>> update_rating(songs, "Hey Jude", 4)
True
>>> update_rating(songs, "Unknown Song", 4)
False
"""
# Implementation will come later...
pass
list, str, int) catch type mismatches earlybool) makes it clear how to check for successAudrey: "How about something that combines rating and play count? Like rating × log(play_count + 1)?"Mai: "Perfect! Let’s write out the contract first, before any code:"
def compute_popularity(song: list) -> float:
"""
Calculates a song's popularity score based on rating and play count.
The score is: rating * log(play_count + 1)
This means:
- A 5-star song with 0 plays scores 5 * log(1) = 0
- A 5-star song with 100 plays scores 5 * log(101) ≈ 23.0
Args:
song: A list [title, rating, play_count] where:
- rating is in [1..5]
- play_count is >= 0
Returns:
A float value >= 0, higher means more popular.
Raises:
ValueError: If rating or play_count are invalid.
Example:
>>> compute_popularity(["Hey Jude", 5, 100])
23.0
"""
# We'll implement this in later chapters
pass
def process_data(data: list, threshold: float) -> dict:
"""
Brief description of function's purpose.
Args:
data: Description of data parameter and constraints
threshold: Description and valid range
Returns:
Description of return value
Raises:
ValueError: When and why this might occur
TypeError: If input types are wrong
Examples:
>>> process_data([1, 2, 3], 0.5)
{'above': 2, 'below': 1}
"""
# In Python, we document our contract in comments
def update_rating(song_title: str, new_rating: int) -> bool:
"""
Updates a song's rating if it exists in our library.
Args:
song_title: Name of song (must not be empty)
new_rating: New rating (must be 1-5)
Returns:
True if song was found and updated
"""
# Implementation will come later...
pass
// In Java, some rules are enforced by the language
public boolean updateRating(String songTitle, int newRating) {
// Java ensures songTitle can only be text
// and newRating can only be a whole number
// Implementation will come later...
return false;
}
song_title: str) in a Python signature will cause a runtime error if a different type is passed.True.
False.
