B 2.5 Visualising File Operations - Worksheet - Python

Name: ___________________________________________________________________ Date: _____________________  

Part 1: The Mental Model

In Python, when you open a file, imagine an invisible "cursor" (like the blinking line in a Word document) that points to where the computer will read or write next.

The Golden Rule: You cannot read what is behind the cursor without moving it back.

Part 2: The "Ghost File" Scenario

Analyse the following code snippet. It runs without errors, but the variable content ends up empty.

# Code Snippet A
file = open("my_data.txt", "w+")      # Open for reading AND writing
file.write("Hello World")             # Write data
content = file.read()                 # Try to read data
print(f"Data found: {content}")       # Print result
file.close()

Task 1: Draw the Cursor. Below is a representation of the file buffer after line 2 (file.write("Hello World")) runs. Draw an arrow ^ showing where the "file cursor" is currently sitting.

| H | e | l | l | o |   | W | o | r | l | d |

Task 2: The Logic Error. Explain why file.read() returns an empty string in the code above.

Part 3: Fixing the Bug

There are two ways to fix the "Ghost File" bug. Write the missing line of code for each solution.

Solution A: The "Seek" Method: Move the cursor back to the start manually before reading.

file.write("Hello World")
# [Write the missing line below]
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content = file.read()

Solution B: The "Close & Reopen" Method Save the data properly, close the file, and open it again in a different mode.

file = open("my_data.txt", "w")
file.write("Hello World")
# [Write the missing lines below]
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content = file.read()

Part 4: Challenge - The "Append" Trap A student wants to add a new score to a list of high scores. They run this code:

file = open("scores.txt", "w")  # Danger!
file.write("Player1: 500")
file.close()

What happens to the old scores that were already in the file? 

[ ] They are moved to the bottom. 

[ ] They are kept safely at the top. 

[ ] They are completely deleted.

How should line 1 be changed to fix this?

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