Decorators Advanced

Decorator with Parameters

  1. # decorator factory
  2. def repeat(times):
  3.     def decorator(func):
  4.         def wrapper(*args):
  5.             for _ in range(times):
  6.                 result = func(*args)
  7.             return result
  8.         return wrapper
  9.     return decorator
  10. @repeat(times=3)
  11. def greet():
  12.     print("Hello")
  13. greet()
  14. #ans: Hello (3 times)

Timing Decorator

  1. import time
  2. # measure execution time
  3. def timer(func):
  4.     def wrapper(*args, **kwargs):
  5.         start = time.time()
  6.         result = func(*args, **kwargs)
  7.         end = time.time()
  8.         print(f"{func.__name__}: {end-start}s")
  9.         return result
  10.     return wrapper
  11. @timer
  12. def slow():
  13.     time.sleep(1)

Caching Decorator

  1. from functools import wraps
  2. # simple cache
  3. def cache(func):
  4.     cached = {}
  5.     @wraps(func)
  6.     def wrapper(*args):
  7.         if args in cached:
  8.             return cached[args]
  9.         result = func(*args)
  10.         cached[args] = result
  11.         return result
  12.     return wrapper
  13. @cache
  14. def fibonacci(n):
  15.     if n < 2:
  16.         return n
  17.     return fibonacci(n-1) + fibonacci(n-2)

Authentication Decorator

  1. # check permission
  2. def require_auth(func):
  3.     def wrapper(*args, **kwargs):
  4.         if not is_authenticated():
  5.             raise PermissionError()
  6.         return func(*args, **kwargs)
  7.     return wrapper
  8. @require_auth
  9. def sensitive_operation():
  10.     return "Secret"

Exercises - Part 1

  1. # decorator with args?
  2. def repeat(n):
  3.     def decorator(func):
  4.         def wrapper():
  5.             for _ in range(n):
  6.                 func()
  7.         return wrapper
  8.     return decorator
  9. @repeat(2)
  10. def func():
  11.     print("Hi")
  12. func()
  13. #ans: Hi (twice)

Exercises - Part 2

  1. # lru_cache?
  2. from functools import lru_cache
  3. @lru_cache(maxsize=128)
  4. def fib(n):
  5.     if n < 2:
  6.         return n
  7.     return fib(n-1) + fib(n-2)
  8. #ans: built-in caching

Exercises - Part 3

  1. # multiple decorators with args?
  2. @decorator1(arg1)
  3. @decorator2(arg2)
  4. def func():
  5.     pass
  6. #ans: both decorators get args

Exercises - Part 4

  1. # decorator counting calls?
  2. def count_calls(func):
  3.     def wrapper(*args):
  4.         wrapper.calls += 1
  5.         return func(*args)
  6.     wrapper.calls = 0
  7.     return wrapper
  8. @count_calls
  9. def func():
  10.     pass
  11. func()
  12. func.calls
  13. #ans: 1

Exercises - Part 5

  1. # retry decorator?
  2. def retry(max_attempts):
  3.     def decorator(func):
  4.         def wrapper(*args):
  5.             for attempt in range(max_attempts):
  6.                 try:
  7.                     return func(*args)
  8.                 except:
  9.                     if attempt == max_attempts-1:
  10.                         raise
  11.         return wrapper
  12.     return decorator

Exercises - Part 6

  1. # validation decorator?
  2. def validate(type_):
  3.     def decorator(func):
  4.         def wrapper(arg):
  5.             if not isinstance(arg, type_):
  6.                 raise TypeError()
  7.             return func(arg)
  8.         return wrapper
  9.     return decorator
  10. @validate(int)
  11. def double(x):
  12.     return x * 2

Exercises - Part 7

  1. # property as decorator?
  2. class MyClass:
  3.     @property
  4.     def value(self):
  5.         return 5
  6. #ans: property is a decorator

Exercises - Part 8

  1. # classmethod as decorator?
  2. class MyClass:
  3.     @classmethod
  4.     def method(cls):
  5.         pass
  6. #ans: classmethod is a decorator

Exercises - Part 9

  1. # staticmethod as decorator?
  2. class MyClass:
  3.     @staticmethod
  4.     def method():
  5.         pass
  6. #ans: staticmethod is a decorator

Exercises - Part 10

  1. # decorator preserving signature?
  2. from functools import wraps
  3. def decorator(func):
  4.     @wraps(func)
  5.     def wrapper(*args, **kwargs):
  6.         return func(*args, **kwargs)
  7.     return wrapper
  8. #ans: preserves func signature

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