Python File Handling and Exception Handling: A Strong Guide

File handling and exception handling are essential concepts in Python, enabling developers to work with files efficiently and manage runtime errors gracefully. In this blog, we will explore how to handle files in Python and manage exceptions using try-except blocks.

Python File Handling
Exception Handling in Python
- Basic Exception Handling
- Using else and finally
Conclusion

Python File Handling

Python provides built-in functions to work with files. The open() function is used to open files, while various modes allow us to read, write, and append data.

Opening a File

The open() function accepts two parameters: filename and mode.

file = open("example.txt", "r")  # Opens the file in read mode

File Modes

Mode	Description
`"r"`	Read mode (default). Opens a file for reading.
`"w"`	Write mode. Creates a new file or truncates an existing file.
`"a"`	Append mode. Adds content to the end of an existing file.
`"x"`	Exclusive creation mode. Fails if the file already exists.
`"b"`	Binary mode. Used for non-text files like images.
`"r+"`	Read and write mode. Does not truncate the file.
`"w+"`	Write and read mode. Truncates the file before writing.

Reading from a File

Python provides multiple ways to read files:

with open("example.txt", "r") as file:
    content = file.read()  # Reads entire content
    print(content)

Writing to a File

To write data to a file, use write (w) or append (a) mode:

with open("example.txt", "w") as file:
    file.write("Hello, Python!")

Appending content:

with open("example.txt", "a") as file:
    file.write("\nAppending new content.")

Writing to a CSV File

Python provides the csv module to handle CSV files:

import csv

data = [["Name", "Age", "City"],
        ["Alice", 25, "New York"],
        ["Bob", 30, "Los Angeles"]]

with open("data.csv", "w", newline='') as file:
    writer = csv.writer(file)
    writer.writerows(data)

Writing to a JSON File

Python’s json module allows easy JSON handling:

import json

data = {"name": "Alice", "age": 25, "city": "New York"}

with open("data.json", "w") as file:
    json.dump(data, file, indent=4)

Why Use `with open()` Instead of `open()`?

Using with open() is recommended because:

Automatic Resource Management: It ensures that the file is automatically closed when the block is exited, even if an error occurs.
Prevents Resource Leaks: Not closing files manually can lead to resource exhaustion and unexpected behavior.
Cleaner Code: The with statement provides better readability and removes the need for explicit close() calls.

Example:

# Recommended approach
with open("example.txt", "r") as file:
    content = file.read()

# Not recommended approach (requires manual close)
file = open("example.txt", "r")
content = file.read()
file.close()

Closing a File

Python automatically closes a file when using with open(). However, when using open() manually, always close it:

file = open("example.txt", "r")
print(file.read())
file.close()  # Always close the file to free resources

Exception Handling in Python

Python handles runtime errors using try-except blocks to prevent crashes and manage errors efficiently.

Basic Exception Handling

try:
    num = int(input("Enter a number: "))
    result = 10 / num
    print("Result:", result)
except Exception as e:
    print(e)

Using `else` and `finally`

This both can be used to add extra feature to the try and except

else: Runs if no exception occurs.
finally: Runs regardless of an exception.

try:
    with open("example.txt", "r") as file:
        content = file.read()
except Exception as e:
    print(e)
else:
    print("File read successfully:", content)
finally:
    print("Execution completed.")

Conclusion

Python’s file handling and exception handling mechanisms provide powerful tools for working with files safely and managing errors effectively. Always use with open() to handle files and wrap critical operations in try-except blocks to make your code robust and error-free.

Want to explore more? Try building a simple log file system that stores error messages in a file whenever an exception occurs. Happy coding!

Python File Handling and Exception Handling: A Strong Guide

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