Functions and Files Checkpoint

1. Write a function with a default argument.
2. Explain the difference between print and return.
3. Split a calculator into functions.
4. Read a file line by line.
5. Append a record to a file.
6. Save and load JSON.
7. Handle invalid numeric input.
8. Explain why with open(...) is useful.
9. Create and import a custom module.
10. Refactor a previous project into multiple functions.