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← Python Basics
○Welcome to Python○Demo: Print a Message○Exercise: Print an Announcement○Demo: Names and Values○Exercise: Label a Station○Demo: Inspect Data Types○Exercise: Record Supplies✦Module Quiz
○Demo: Calculate with Numbers○Exercise: Calculate a Bus Cost○Demo: Format a Message○Exercise: Format an Invoice○Demo: Convert Text to Numbers○Exercise: Convert Measurements○Demo: A Prefilled User Response○Exercise: Build a Workshop Ticket✦Module Quiz
○Compare and branch○Exercise: Choose a shelf sign○Repeat with while○Exercise: Charge a device○Count with for and range○Exercise: Mark bus stops○Skip with continue, stop with break○Exercise: Admit visitors○Project: Workshop sign-in✦Module Quiz
○Define and Call: Demo○Exercise: Define and Call○Parameters and Return: Demo○Exercise: Parameters and Return○Defaults and Keywords: Demo○Exercise: Defaults and Keywords○Local Scope: Demo○Exercise: Local Scope○Project: Workshop Receipts✦Module Quiz
○Index a Text Code○Exercise: Read Badge Edges○Slice a Route Label○Exercise: Slice Ticket Fields○Clean a Message with Methods○Exercise: Standardize a Notice○Format a Card with an f-String○Exercise: Make a Market Sign✦Module Quiz
○Create and Index a Supply List○Exercise: Build a Queue○Change a Playlist○Exercise: Update Orders○Loop and Slice a Route○Exercise: Pack Deliveries○Read a Fixed Tuple Record○Exercise: Read a Session Record✦Module Quiz
○Look Up and Update a Dictionary○Exercise: Update a Contact○Loop Through Dictionary Entries○Exercise: Write a Receipt○Keep Unique Visitors in a Set○Exercise: Compare Club Groups○Demo: Summarize Library Visits○Exercise: Build a Market Roster✦Module Quiz
●Tracebacks and a Safe Count Demo○Exercise: Recover Ticket Counts○Write and Read a Browser File Demo○Exercise: Save and Read a Message○Mini Project: Attendance Log✦Module Quiz
○Import Math: Demo○Exercise: Import Math○Local Module: Demo○Exercise: Local Module○Packages and Dotted Imports✦Module Quiz
○Recursion and a Base Case Demo○Exercise: Recursive Ticket Sum○Lambda, Map, and Filter Demo○Exercise: Clean Badge Names✦Module Quiz
○Classes, Objects, and Enums to Recognize○Final Project: Workshop Board✦Module Quiz

Tracebacks and a Safe Count Demo

The supply desk receives a count as text. A traceback ending in ValueError tells you that int("unknown") could not convert it. Read the final line for the error type, then the indicated line for the failing operation; a SyntaxError must be repaired before the program can run.

The complete safe_count function catches only ValueError; unrelated errors should still surface. Edit main.py: change the fallback for invalid text from 0 to -1. Press Run to see -1 for "unknown", then Submit. The next lesson transfers this pattern to ticket quantities.

Your Task

  1. Change only the ValueError fallback to -1; valid numeric text must still become an integer.
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Press Run to execute your code.