哪些函数不能在 Python 中修饰？

Question

In a college test or interview question setting, how could you answer:

What functions can't be decorated in Python?

It's beneficial to demonstrate depth of knowledge, so I would begin by briefly describing the uses of decorators in Python. What are their limitations?

I've read the Decorator pattern Wiki and can't find any anti-patterns.

A. Decorator uses

1. Decorators in Python are useful to extend the functionality of module functions, class methods, and classes themselves. For example, using a debug logging wrapper to a function or a dynamic programming cache:

@functools.lru_cache(maxsize=128)
def fibonacci(n=10):
    ...

2. A class can also act as a decorator (if you implement the __init__() and __call__() methods).

3. A decorator can be wrapped to allow passing of arguments. It can also be chained with other decorators.

B. When can't you use a decorator

1. You cannot use a decorator for variable assignments, calling functions etc. They are only used when defining a function/class/method.

2. You may not want to use a decorator on a recursive function as it effectively halves the maximum recursion depth (as suggested by @jasonharper).

Are there any other cases when a decorator couldn't ( or shouldn't ) be used?

Answer 1

Maybe I got it wrong, but if you are not using syntactic sugar of the decorator ("@my_decorator"), then it's used via assigning a decorated function to a function you would like to decorate. So technically speaking, decorator can be used in assigning, not only in function definition, but function assigning to the other function:

# let's create a simple decorator
def mydecorator(decorated_func):
    def wrapped(*args, **kwargs):
        print("Something happened in decorator!")
        return decorated_func(*args, **kwargs)
    return wrapped


# let's use decorator with syntactic sugar "@"
@mydecorator
def myfunc(myarg):
    print("my function", myarg)


# just simple function
def mysecond_func(myarg):
    print("my second function", myarg)

# let's decorate the second function with the same decorator,
# but without using syntactic sugar;
# it's identical with the first example with "@"
mysecond_func = mydecorator(mysecond_func)