File Handling in Python- Python Course

File Handling in Python

Reading and Writing Text Files in Python

Python provides simple methods to read and write text files. These operations are essential for saving data, logs, configurations, or exports.

Writing to a file

f = open("file.txt", "w")
f.write("Hello, John!")
f.close()

Reading from a file

f = open("file.txt", "r")
content = f.read()
print(content)
f.close()

File modes

"r"  # read
"w"  # write (overwrite)
"a"  # append
"r+" # read and write

Opening files with with open() in Python

The with open() statement is the safest and recommended way to work with files in Python. It automatically handles file closure, even if errors occur.

Writing with with open()

with open("file.txt", "w") as f:
    f.write("Hello, John!")

Reading with with open()

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

Reading line by line

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

Handling Exceptions with try - except - finally

In Python, errors can be gracefully handled using try, except, and finally blocks. These allow controlling program behavior in case of exceptions.

Simple example

try:
    f = open("file_not_existing.txt", "r")
except FileNotFoundError:
    print("The file was not found.")
finally:
    print("The operation has ended.")

Explanations

• try: code that may raise an exception.
• except: code that runs if an exception occurs.
• finally: code that runs whether or not an exception occurred.

Multiple types of exceptions

try:
    x = int(input("Enter a number: "))
    result = 10 / x
except ValueError:
    print("You did not enter a valid number.")
except ZeroDivisionError:
    print("Division by zero is not allowed.")
finally:
    print("Calculation done.")

Saving Data to Files

To save data to files, we use "w" (write) or "a" (append) mode. These create the file if it does not exist.

Simple write

with open("date.txt", "w") as f:
    f.write("Name: John\nAge: 25")

Appending content

with open("date.txt", "a") as f:
    f.write("\nCity: Bristol")

Reading and Writing JSON and CSV

Python offers native support for working with .json and .csv files, commonly used in web applications, databases, and data analysis.

JSON - JavaScript Object Notation

import json

# Save to JSON file
data = {"name": "John", "age": 25}
with open("date.json", "w") as f:
    json.dump(data, f)

# Read from JSON file
with open("date.json", "r") as f:
    loaded = json.load(f)
    print(loaded)

CSV - Comma-Separated Values

import csv

# Write to CSV file
with open("date.csv", "w", newline="") as f:
    writer = csv.writer(f)
    writer.writerow(["Name", "Age"])
    writer.writerow(["John", 25])

# Read from CSV file
with open("date.csv", "r") as f:
    reader = csv.reader(f)
    for line in reader:
        print(line)

Practical Exercises

Practice working with files in Python through the following challenges. You can test the code directly in your editor.

1. Write a file with your data

with open("profil.txt", "w") as f:
    f.write("Name: John\nAge: 25\nCity: London")

2. Read and display the file content

with open("profil.txt", "r") as f:
    print(f.read())

3. Save a dictionary in JSON format

import json

data = {"name": "John", "email": "John@example.com"}
with open("profil.json", "w") as f:
    json.dump(data, f)

4. Create a CSV file with multiple users

import csv

users = [
    ["Name", "Age", "City"],
    ["John", 25, "London"],
    ["Maria", 30, "Manchester"],
    ["Andrew", 22, "Bristol"]
]

with open("utilizatori.csv", "w", newline="") as f:
    writer = csv.writer(f)
    writer.writerows(users)

5. Handle an exception when reading a non-existent file

try:
    with open("inexistent.txt", "r") as f:
        print(f.read())
except FileNotFoundError:
    print("The file does not exist.")

🧠 Quiz - Files and Exception Handling in Python