decator operator Interview Questions and Answers

1. What is a decorator?

   • Answer: A decorator is a design pattern in Python that allows you to modify or enhance a function or method's behavior without modifying its core functionality. It's achieved by wrapping the original function with another function, often adding features like logging, access control, or timing.

2. How do you define a decorator in Python?

   • Answer: A decorator is typically defined as a function that takes another function as input and returns a modified version of that function.

3. Explain the `@` symbol in decorators.

   • Answer: The `@` symbol is syntactic sugar in Python. It's a shorthand way to apply a decorator to a function. `@decorator_function` is equivalent to `function = decorator_function(function)`.

4. What are the benefits of using decorators?

   • Answer: Decorators promote code reusability, readability, and maintainability. They help keep your code DRY (Don't Repeat Yourself) by centralizing common functionality.

5. Give an example of a simple decorator that adds logging.

   • Answer: ```python import functools def log_execution(func): @functools.wraps(func) # Preserves original function metadata def wrapper(*args, **kwargs): print(f"Executing function: {func.__name__}") result = func(*args, **kwargs) print(f"Function {func.__name__} finished.") return result return wrapper @log_execution def my_function(a, b): return a + b print(my_function(2, 3)) ```

6. Explain the use of `functools.wraps` in decorators.

   • Answer: `functools.wraps` is a decorator itself! It helps preserve the metadata (like the function's name and docstring) of the original function after it's been wrapped. Without it, introspection on the decorated function would reveal the wrapper function, not the original.

7. How can you pass arguments to a decorator?

   • Answer: You can create a decorator factory – a function that returns a decorator. This factory function takes the arguments, and the returned decorator then applies those arguments to the wrapped function.

8. Create a decorator that takes an argument and repeats a function's execution.

   • Answer: ```python import functools def repeat(num_times): def decorator(func): @functools.wraps(func) def wrapper(*args, **kwargs): for _ in range(num_times): result = func(*args, **kwargs) return result return wrapper return decorator @repeat(3) def greet(name): print(f"Hello, {name}!") greet("World") ```

9. What are class decorators?

   • Answer: Class decorators work similarly to function decorators but are applied to classes. They can modify class behavior by adding methods or modifying existing ones.

10. Give an example of a class decorator.

    • Answer: ```python def singleton(cls): instances = {} def getinstance(*args, **kwargs): if cls not in instances: instances[cls] = cls(*args, **kwargs) return instances[cls] return getinstance @singleton class MyClass: pass a = MyClass() b = MyClass() print(a is b) # Output: True (they are the same instance) ```

11. Explain the concept of decorator chaining.

    • Answer: Decorator chaining involves applying multiple decorators to a single function. The decorators are applied in the order they are listed, with the innermost decorator being applied first.

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