Python Interview Questions

Handling file exceptions in Python is essential to ensure your program can deal with unexpected situations, such as a file not being found, lacking permissions to read or write a file, or encountering errors while processing file data. Python provides a robust way to handle these scenarios using try, except, else, and finally blocks. Here's how you can handle file exceptions effectively:

Basic Exception Handling

Use try and except blocks to catch exceptions when working with files.

Example:

try:
    with open('nonexistent_file.txt', 'r') as file:
        content = file.read()
except FileNotFoundError:
    print("File not found. Please check the file path.")
except PermissionError:
    print("Permission denied. You do not have the right permissions to access this file.")
except Exception as e:
    print(f"An unexpected error occurred: {e}")

In this example:

• FileNotFoundError is caught if the file does not exist.
• PermissionError is caught if there are issues with file access permissions.
• Exception catches any other exceptions that may occur, providing a generic error message.

Using else Block

The else block can be used to run code that should execute only if no exceptions were raised.

Example:

try:
    with open('example.txt', 'r') as file:
        content = file.read()
except FileNotFoundError:
    print("File not found. Please check the file path.")
except PermissionError:
    print("Permission denied. You do not have the right permissions to access this file.")
except Exception as e:
    print(f"An unexpected error occurred: {e}")
else:
    print("File read successfully.")
    print(content)

In this example:

• The else block runs only if the file is read successfully without any exceptions.

Using finally Block

The finally block can be used to execute code that should run no matter what, such as cleaning up resources.

Example:

try:
    with open('example.txt', 'r') as file:
        content = file.read()
except FileNotFoundError:
    print("File not found. Please check the file path.")
except PermissionError:
    print("Permission denied. You do not have the right permissions to access this file.")
except Exception as e:
    print(f"An unexpected error occurred: {e}")
else:
    print("File read successfully.")
    print(content)
finally:
    print("Finished file operation.")

In this example:

• The finally block always runs, regardless of whether an exception was raised. It is useful for cleanup actions.

Handling Specific Exceptions

Python provides several built-in exceptions for file operations. Some common ones include:

• FileNotFoundError: Raised when a file or directory is requested but doesn’t exist.
• PermissionError: Raised when trying to run an operation without the adequate access rights.
• IOError: Raised when an I/O operation (such as a print statement, the built-in open() function, or a method of a file object) fails.
• IsADirectoryError: Raised when a file operation (like open) is requested on a directory.

Example of Handling Multiple Specific Exceptions

try:
    with open('example.txt', 'r') as file:
        content = file.read()
except FileNotFoundError:
    print("File not found. Please check the file path.")
except PermissionError:
    print("Permission denied. You do not have the right permissions to access this file.")
except IsADirectoryError:
    print("Expected a file but found a directory.")
except Exception as e:
    print(f"An unexpected error occurred: {e}")
else:
    print("File read successfully.")
    print(content)
finally:
    print("Finished file operation.")

In this example:

• Multiple specific exceptions are handled to provide precise error messages.

Summary

• try: The block where you write the code that might raise an exception.
• except: The block where you handle the exceptions.
• else: The block that runs if no exceptions are raised.
• finally: The block that always runs, regardless of whether an exception was raised.

Using these blocks effectively allows you to handle file exceptions gracefully, ensuring your program can respond to unexpected situations without crashing.