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Puzzle 20: Explanation

Explore how Python context managers function using the with statement to manage resources like files and locks. Understand the role of __enter__ and __exit__ methods, including how exceptions like ZeroDivisionError can be suppressed, enhancing your ability to handle resource management and exceptions in Python code.

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Try it yourself

Try executing the code below to verify the results:

Python 3.8
class timer:
    def __init__(self, name):
        self.name = name
    def __enter__(self):
        ...  
    def __exit__(self, exc_type, exc_value, traceback):
        result = 'OK' if exc_type is None else 'ERROR'
        print(f'{self.name} - {result}')
        return True
with timer('div'):
    1 / 0

Explanation

Most people expect to see a ZeroDivisionError exception in the output of the above code. The timer syntax in the code above is a context manager. A context manager is used with the with statement and is usually for managing resources. For example, the snippet with open('input.txt') will make sure that the file is closed after the code inside the ...