File Handling (Reading, Writing, Appending)

Programs often need to store data permanently — after the program closes, the data should still be available the next time it runs. File handling allows programs to read from and write to text files. This is a key topic for GCSE Computer Science (AQA 3.2 / OCR J277 2.2).

---

Why Use Files?

Variables only exist while a program is running. When the program ends, all variable data is lost. Files provide persistent storage — data saved to a file remains available after the program closes.

Common uses of file handling:

• Saving high scores in a game
• Storing user account details
• Logging events or errors
• Reading configuration settings

---

File Operations

There are three main file operations:

Operation	Description	Pseudocode	Python mode
Read	Opens a file and reads its contents	OPENREAD	"r"
Write	Creates a new file (or overwrites existing) and writes data	OPENWRITE	"w"
Append	Opens an existing file and adds data to the end	OPENAPPEND	"a"

Warning: OPENWRITE / mode "w" will overwrite the entire file. If you want to add to an existing file, use append.

---

Writing to a File

Pseudocode

file ← OPENWRITE("scores.txt")
file.WRITELINE("Alice,85")
file.WRITELINE("Bob,72")
file.CLOSE()

Python

file = open("scores.txt", "w")
file.write("Alice,85\n")
file.write("Bob,72\n")
file.close()

Or using a with statement (recommended in Python — automatically closes the file):

with open("scores.txt", "w") as file:
    file.write("Alice,85\n")
    file.write("Bob,72\n")

Note: In Python, write() does not automatically add a newline — you must include \n yourself.

---

Reading from a File

Reading the Entire File

with open("scores.txt", "r") as file:
    contents = file.read()
    print(contents)

Reading Line by Line

Pseudocode

file ← OPENREAD("scores.txt")
WHILE NOT file.ENDOFFILE()
    line ← file.READLINE()
    OUTPUT line
ENDWHILE
file.CLOSE()

Python

with open("scores.txt", "r") as file:
    for line in file:
        print(line.strip())

The .strip() method removes the trailing newline character from each line.

Reading All Lines into a List

with open("scores.txt", "r") as file:
    lines = file.readlines()
    for line in lines:
        print(line.strip())

---

Appending to a File

Appending adds new data to the end of an existing file without deleting its current contents.

Pseudocode

file ← OPENAPPEND("scores.txt")
file.WRITELINE("Charlie,91")
file.CLOSE()

Python

with open("scores.txt", "a") as file:
    file.write("Charlie,91\n")

---

Working with CSV-Style Data

Files often store data in a structured format with fields separated by commas (CSV). You can split each line to extract individual values:

with open("scores.txt", "r") as file:
    for line in file:
        parts = line.strip().split(",")
        name = parts[0]
        score = int(parts[1])
        print(f"{name} scored {score}")

Searching a File

target = input("Enter name to search for: ")
found = False
with open("scores.txt", "r") as file:
    for line in file:
        parts = line.strip().split(",")
        if parts[0] == target:
            print(f"Found: {parts[0]} scored {parts[1]}")
            found = True
if not found:
    print("Name not found")

---

File Handling Lifecycle

flowchart TD
    A[Start] --> B{Choose mode}
    B -->|Read| C[OPENREAD filename]
    B -->|Write| D[OPENWRITE filename]
    B -->|Append| E[OPENAPPEND filename]
    C --> F[READLINE in loop]
    D --> G[WRITELINE data]
    E --> G
    F --> H{End of file?}
    H -->|No| F
    H -->|Yes| I[CLOSE file]
    G --> I
    I --> J[End]

---

Pseudocode Summary Table

Operation	Pseudocode
Open for reading	file ← OPENREAD("filename.txt")
Open for writing	file ← OPENWRITE("filename.txt")
Open for appending	file ← OPENAPPEND("filename.txt")
Read a line	line ← file.READLINE()
Write a line	file.WRITELINE("data")
Check end of file	file.ENDOFFILE()
Close the file	file.CLOSE()

---

Error Handling with Files

Files may not always exist or be accessible. In Python, you can handle this with try...except:

try:
    with open("scores.txt", "r") as file:
        contents = file.read()
        print(contents)
except FileNotFoundError:
    print("Error: File not found.")

Exam Tip: In pseudocode you are unlikely to be asked about error handling with files, but in Python-based questions showing try...except demonstrates good practice.

---

Practical Example: A Simple Address Book

def add_contact(name, phone):
    with open("contacts.txt", "a") as file:
        file.write(f"{name},{phone}\n")
    print("Contact added.")

def view_contacts():
    try:
        with open("contacts.txt", "r") as file:
            for line in file:
                parts = line.strip().split(",")
                print(f"Name: {parts[0]}, Phone: {parts[1]}")
    except FileNotFoundError:
        print("No contacts found.")

# Main menu
while True:
    choice = input("1) Add  2) View  3) Quit: ")
    if choice == "1":
        name = input("Name: ")
        phone = input("Phone: ")
        add_contact(name, phone)
    elif choice == "2":
        view_contacts()
    elif choice == "3":
        break

---

Common Exam Mistakes

1. Forgetting to close the file — always use file.CLOSE() in pseudocode or a with statement in Python.
2. Using write mode when you mean append — "w" erases the file first.
3. Not stripping newlines when reading — line.strip() removes trailing \n.
4. Not handling the case where the file doesn't exist when reading.

---

Summary

• Reading ("r") retrieves data from an existing file.
• Writing ("w") creates a new file or overwrites an existing one.
• Appending ("a") adds data to the end of an existing file.
• Always close files after use (or use Python's with statement).
• Data in files often uses a delimiter (e.g. comma) — use split() to extract fields.
• Use strip() to remove trailing newline characters when reading.

---

Extended Worked Examples

Example 1: Writing a high-score table

scores = [
    ("Ali", 95),
    ("Bea", 88),
    ("Cai", 77),
]

with open("highscores.txt", "w") as file:
    for name, score in scores:
        file.write(f"{name},{score}\n")

After running, highscores.txt contains:

Ali,95
Bea,88
Cai,77

Example 2: Reading back and computing the top scorer

top_name = ""
top_score = -1

with open("highscores.txt", "r") as file:
    for line in file:
        parts = line.strip().split(",")
        if len(parts) == 2:
            name = parts[0]
            score = int(parts[1])
            if score > top_score:
                top_score = score
                top_name = name

print(f"Top: {top_name} with {top_score}")

Expected output: Top: Ali with 95

Example 3: Appending a new record

def record_score(name, score):
    with open("highscores.txt", "a") as file:
        file.write(f"{name},{score}\n")

record_score("Dia", 91)