PYTHON FILE HANDLING

Python uses the open() function to open a file. The basic syntax is:

file = open("data.txt", "r")

Here, data.txt is the file name and "r" means read mode.

Python provides different modes depending on what you want to do with the file.

The read() method reads the complete contents of a file.

file = open("employees.txt", "r")

content = file.read()

print(content)

file.close()

The readline() method reads one line at a time.

file = open("employees.txt", "r")

line = file.readline()

print(line)

file.close()

readlines() returns all lines as a list.

file = open("employees.txt", "r")

lines = file.readlines()

for line in lines:
    print(line.strip())

file.close()

The w mode writes data to a file. If the file does not exist, Python creates it.

file = open("welcome.txt", "w")

file.write("Welcome to Python File Handling!")

file.close()

The a mode adds new data at the end of the existing file.

file = open("employees.txt", "a")

file.write("\nNeha - HR")

file.close()

The recommended way to work with files is using with open(). Python automatically closes the file after the block finishes.

with open("employees.txt", "r") as file:
    content = file.read()
    print(content)

A school application can store student information in a text file.

student = {
    "name": "Rahul",
    "age": 21,
    "course": "Python"
}

with open("student.txt", "w") as file:
    file.write(f"Name: {student['name']}\n")
    file.write(f"Age: {student['age']}\n")
    file.write(f"Course: {student['course']}\n")

print("Student record saved successfully.")

Applications often store login activity in log files for auditing and troubleshooting.

username = "rahul"

with open("login.log", "a") as file:
    file.write(f"User {username} logged in successfully.\n")

print("Login activity recorded.")

A banking application can maintain a simple transaction history using a file.

amount = 5000
account = "ACC1001"

with open("transactions.txt", "a") as file:
    file.write(
        f"Account: {account}, Deposit: ₹{amount}\n"
    )

print("Transaction recorded.")

An online shopping application can save order information into a file.

order_id = "ORD1001"
product = "Laptop"
price = 55000

with open("orders.txt", "a") as file:
    file.write(
        f"{order_id} | {product} | ₹{price}\n"
    )

print("Order saved successfully.")

The os.path.exists() function can be used to check whether a file exists.

import os

filename = "employees.txt"

if os.path.exists(filename):
    print("File exists.")
else:
    print("File does not exist.")

The x mode creates a new file. If the file already exists, Python raises an error.

try:
    with open("new_report.txt", "x") as file:
        file.write("Monthly Report")
        
    print("File created successfully.")

except FileExistsError:
    print("File already exists.")

An attendance system can append an employee's attendance information every day.

employee_id = "EMP101"
date = "2026-09-20"
status = "Present"

with open("attendance.txt", "a") as file:
    file.write(
        f"{employee_id} | {date} | {status}\n"
    )

print("Attendance saved.")

When a file does not exist, opening it in read mode raises FileNotFoundError. We can handle it using try-except.

try:
    with open("customer.txt", "r") as file:
        data = file.read()
        print(data)

except FileNotFoundError:
    print("Customer file was not found.")

Python can provide information such as file name, mode, and whether the file is closed.

file = open("data.txt", "r")

print("File name:", file.name)
print("File mode:", file.mode)
print("Is closed:", file.closed)

file.close()

print("Is closed:", file.closed)

Binary mode is useful for files such as images, PDFs, audio, and other non-text data.

with open("photo.jpg", "rb") as file:
    data = file.read()

print("Binary data loaded.")
print("Bytes:", len(data))

A binary file can be copied by reading its bytes and writing them into another file.

with open("original.jpg", "rb") as source:
    data = source.read()

with open("backup.jpg", "wb") as destination:
    destination.write(data)

print("File copied successfully.")

The following example demonstrates how a small application can save customer records into a file and later display them.

def add_customer(customer_id, name, phone):
    with open("customers.txt", "a") as file:
        file.write(
            f"{customer_id},{name},{phone}\n"
        )

    print("Customer added successfully.")


def show_customers():
    try:
        with open("customers.txt", "r") as file:
            print("\nCustomer Records:")

            for line in file:
                customer_id, name, phone = line.strip().split(",")

                print(
                    f"ID: {customer_id} | "
                    f"Name: {name} | "
                    f"Phone: {phone}"
                )

    except FileNotFoundError:
        print("No customer records found.")


add_customer("C101", "Rahul", "9876543210")
add_customer("C102", "Priya", "9123456780")

show_customers()

• Prefer with open() for automatic file closing.
• Choose the correct file mode before opening a file.
• Use a when existing data must be preserved.
• Use w carefully because it replaces existing content.
• Handle FileNotFoundError when reading files that may not exist.
• Use binary modes such as rb and wb for binary files.
• Use appropriate file paths instead of relying on the current directory.
• For structured application data, consider formats such as JSON or CSV.

Python File Handling

Open • Read • Write • Append • Manage Files with Python