Knowledge Check: Module 24

1. Which mode should you use with `open()` to write to a file, completely overwriting its previous content if it exists?

`'r'` `'a'` `'w'` `'x'`

2. If you want to add new lines to the end of an existing file without deleting its content, which mode should you use?

`'w'` `'r+'` `'a'` (append) `'r'`

3. What is the primary method used on a file object (e.g., `f`) to write a string into the file?

`f.print("text")` `f.append("text")` `f.write("text")` `f.save("text")`

4. What is the main advantage of using the `with open(...) as f:` structure when working with files?

It automatically reads the entire file content. It ensures the file is automatically closed, even if errors occur. It automatically creates the file if it doesn't exist. It makes the file write operations faster.

5. How do you typically represent a newline character when writing to a text file in Python?

`"
"` `"\\n"` `""` `"\\r\\n"` (always)

6. What happens if you use `open('my_new_file.txt', 'w')` and the file `my_new_file.txt` does not exist?

Python raises a `FileNotFoundError`. Python creates the empty file `my_new_file.txt`. It returns `None` instead of a file object. It asks the user for permission to create the file.

7. Consider this code: `with open('data.txt', 'a') as f: f.write("More data")`. If `data.txt` did not exist before running this, what will be the result?

An error will occur because 'a' mode cannot create files. The file `data.txt` will be created and will contain "More data". The file `data.txt` will be created, but it will be empty. Nothing will happen, the operation fails silently.

8. The `f.write()` method expects its argument to be what data type?

An integer (`int`) A list (`list`) A string (`str`) A boolean (`bool`)

9. If you have a list of strings, like `lines = ["First line", "Second line"]`, how would you typically write each string on a new line in a file using `f.write()`?

`f.write(lines)` `f.writelines(lines)` (Note: `writelines` does not add newlines automatically) Use a loop: `for line in lines: f.write(line + "\\n")` `f.write(str(lines))`

10. Forgetting to close a file after writing (when not using `with`) can potentially lead to...?

The file being automatically deleted by Python. Data loss, as written data might not be fully flushed from the buffer to the disk. Faster subsequent read operations. Improved program performance.

Module 24: Writing to Files