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Python Finally and else clauses

In Python, the else and finally clauses in exception handling provide additional ways to manage the flow of your program when exceptions occur. Here’s a detailed look at how they work and examples to illustrate their usage.

The else Clause

The else clause is used to specify a block of code that should run if no exceptions are raised in the try block. It is typically used for code that should only run if the try block succeeds.

Example:

try:
    result = 10 / 2
except ZeroDivisionError:
    print("Error: Division by zero is not allowed.")
else:
    print(f"Result is {result}")

In this example:

  • If the division is successful, the else block executes and prints the result.
  • If a ZeroDivisionError occurs, the except block executes, and the else block is skipped.

The finally Clause

The finally clause is used to specify a block of code that will always be executed, regardless of whether an exception was raised or not. This is useful for cleanup actions like closing files or releasing resources.

Example:

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Error: Division by zero is not allowed.")
finally:
    print("This block will always execute.")

In this example:

  • The finally block executes regardless of whether an exception is raised in the try block or not.

Using else and finally Together

You can use both else and finally clauses in the same try block. Here’s an example to demonstrate how they work together:

Example:

try:
    with open('example.txt', 'r') as file:
        contents = file.read()
except FileNotFoundError:
    print("Error: File not found.")
except IOError:
    print("Error: An I/O error occurred.")
else:
    print("File read successfully:")
    print(contents)
finally:
    print("Finished file operation.")

In this example:

  • The try block attempts to open and read a file.
  • If the file is not found, the FileNotFoundError exception is caught and the corresponding message is printed.
  • If an I/O error occurs, the IOError exception is caught and the corresponding message is printed.
  • If no exceptions are raised, the else block executes, printing the contents of the file.
  • Regardless of the outcome, the finally block executes, printing "Finished file operation."

Summary

  • else Clause: Executes if no exceptions are raised in the try block.
  • finally Clause: Always executes, regardless of whether an exception was raised or not.

Using these clauses allows you to manage your code more effectively, ensuring that you have clearly defined paths for handling both successful and exceptional conditions, along with a guaranteed cleanup mechanism.

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