12.5 💾 Binary File Handling in Python – Class XII CBSE Made Easy

 

📦 What is a Binary File?

A binary file stores data in a format not readable by humans — it’s meant to be interpreted by programs. This is ideal for storing:

• Numbers
• Lists, dictionaries
• User-defined objects

In Python, we use the pickle module to serialize (write) and deserialize (read) objects to/from binary files.

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🛠️ What is Pickling and Unpickling?

Term	Meaning
Pickling	Converting a Python object into a byte stream (saving to file)
Unpickling	Converting a byte stream back to a Python object (loading from file)

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🔧 Importing the Module

import pickle

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📝 Writing to a Binary File (Pickling)

import pickle

data = [101, "Rahul", 91.2]
f = open("student.dat", "wb")  # 'wb' = write binary
pickle.dump(data, f)
f.close()

✔️ pickle.dump(object, file) is used to save the object.

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📖 Reading from a Binary File (Unpickling)

import pickle

f = open("student.dat", "rb")  # 'rb' = read binary
data = pickle.load(f)
print(data)
f.close()

✔️ pickle.load(file) reads and restores the object.

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🔄 Storing Multiple Records

import pickle

f = open("records.dat", "wb")
for i in range(3):
    name = input("Enter name: ")
    marks = float(input("Enter marks: "))
    rec = [name, marks]
    pickle.dump(rec, f)
f.close()

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📂 Reading Multiple Records

import pickle

f = open("records.dat", "rb")
try:
    while True:
        rec = pickle.load(f)
        print(rec)
except EOFError:
    f.close()

🛑 Why try-except? Because pickle.load() raises EOFError when it reaches the end of the file.

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🔍 Updating a Record in a Binary File

1. Read all records.
2. Modify the target.
3. Rewrite all back.

import pickle
f1 = open("records.dat", "rb")
f2 = open("temp.dat", "wb")

try:
    while True:
        rec = pickle.load(f1)
        if rec[0] == "Rahul":
            rec[1] = 95.0  # updating marks
        pickle.dump(rec, f2)
except EOFError:
    f1.close()
    f2.close()

import os
os.remove("records.dat")
os.rename("temp.dat", "records.dat")

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⚠️ Important Points:

• Binary files cannot be opened in text editors.
• Always use 'rb' and 'wb' for binary mode.
• Use try-except to handle end-of-file errors.
• Don’t forget to import pickle before use.

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💡 Example Programs

🔹 Program 1: Write a list of student records to a binary file

students = [["Ravi", 85], ["Anu", 92], ["Mohit", 78]]
with open("stud.dat", "wb") as f:
    for s in students:
        pickle.dump(s, f)

🔹 Program 2: Display all student names who scored above 80

with open("stud.dat", "rb") as f:
    try:
        while True:
            rec = pickle.load(f)
            if rec[1] > 80:
                print(rec[0])
    except EOFError:
        pass

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❓ Practice Questions:

📘 1 Mark – Objective:

1. What is the purpose of pickle.dump()?
2. Which error is raised when end of file is reached?
3. Which file mode is used to read binary files?

✍️ 2 Marks – Short Answer:

1. Differentiate between dump() and load() functions.
2. Why can’t we use read() to read binary files?

💻 3 Marks – Programming:

1. Write a program to store 3 student records using pickle.
2. Write a program to read all records and display those with names starting with 'A'.

🧠 5 Marks – Case-Based:

A file named employee.dat contains multiple employee records in the format: [ID, Name, Salary]. Write a program to:

• Read the file
• Increase salary by 10% for all employees earning below ₹20,000
• Save updated records back to file

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🎯 Tips to Remember:

• Always use binary mode ('wb', 'rb') for binary files.
• Use EOFError to stop reading in a loop.
• Pickling works best with lists, dicts, and even user-defined classes.

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✅ Conclusion

Binary file handling is useful for efficient data storage, especially when you need to store complex data structures. With just a few functions from the pickle module, you can master this high-scoring topic for your CBSE Class XII board exam.