Oppiskele The else and finally Clauses | Advanced Exception Handling

Introduction to the else and finally Clauses

The else and finally clauses provide you with more precise control over error handling in Python. While the try-except block is essential for catching and handling exceptions, adding else and finally allows you to clearly separate code that should run only if no exception occurs from code that must always run, regardless of whether an exception was raised. This structure is especially useful for resource management tasks like working with files or network connections.


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# Demonstrating try-except-else-finally with file operations

try:
    file = open("data.txt", "w")
    file.write("Advanced exception handling in Python.")
except IOError:
    print("Failed to write to file.")
else:
    print("Data written to file successfully.")
finally:
    file.close()
    print("File has been closed.")

When Do else and finally Execute?

In a try-except-else-finally structure:

The try block runs first and contains code that might raise an exception;
If an exception occurs, the except block runs, and the else block is skipped;
If no exception occurs in the try block, the else block runs immediately after the try block;
The finally block always runs, whether or not an exception was raised or handled.

You use the else block for actions that should only happen when no errors occur. The finally block is ideal for cleanup actions, such as closing files or releasing resources, because it executes no matter what happens in the try or except blocks.


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# Example: Using finally for resource cleanup

try:
    file = open("data.txt", "w")
    file.write("Sample data for resource cleanup.")
    print("Data written to file.")
except IOError:
    print("Failed to write to the file.")
finally:
    file.close()
    print("File closed, resources released.")

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