Finally keyword in Python

The finally keyword in Python defines a block of code that executes regardless of whether an exception occurs or not. This makes it useful for cleanup operations like closing files, database connections, or releasing resources.

Syntax

try:
    # Main Python code
except ExceptionType:
    # Optional block to handle specific exceptions
finally:
    # Code that always executes

Example with Exception Handling

Here's an example where a NameError occurs when trying to print an undefined variable ?

try:
    var1 = 'Tutorials'
    # NameError is raised
    print(var2)

# Handle the exception
except NameError:
    print("Variable is not found in local or global scope.")
finally:
    # Regardless of exception generation,
    # this block is always executed
    print('Finally block code here')

Variable is not found in local or global scope.
Finally block code here

Example without Exception Handling

Even when no except block is present, the finally block still executes before the program terminates ?

try:
    var1 = 'Tutorials'
    # NameError is raised
    print(var2)
# No exception handling
finally:
    # This block always executes
    print('Finally block code here')

Finally block code here
Traceback (most recent call last):
  File "<string>", line 4, in <module>
    print(var2)
NameError: name 'var2' is not defined

Common Use Cases

The finally block is commonly used for cleanup operations ?

def read_file(filename):
    file = None
    try:
        file = open(filename, 'r')
        content = file.read()
        return content
    except FileNotFoundError:
        print(f"File {filename} not found")
        return None
    finally:
        if file:
            file.close()
            print("File closed successfully")

# Test with non-existent file
result = read_file('nonexistent.txt')

File nonexistent.txt not found
File closed successfully

Key Points

• The finally block executes whether an exception occurs or not
• It runs even when no except block is present
• Perfect for cleanup operations like closing files or database connections
• Executes before the program terminates due to an unhandled exception

Conclusion

The finally block ensures critical cleanup code always runs, making your programs more robust and preventing resource leaks. Use it whenever you need guaranteed execution of cleanup operations.