我该如何编写随参数而变化的装饰器

Question

I have to write a decorator def that takes a validator def as argument. If the validator returned true it should decorate main to execute some code and if it returned false it should print an error.

I have tried to write two def in decorator with an if statement to return two different defs but it is not working.

the functionality and the logic MUST be exactly like i said because of online judging (validation must be done outside of decorator)

Here's an example:

#define decorator...

def validator(x):
    return x>=0

@decorator(validator)
def f(x):
    return x**0.5

print(f(4)) #should print 2
print(f(-4)) #should print error

Answer 1

Decorators can be written as example

def hello_decorator(func): 
    def inner1(*args, **kwargs): 

        print("before Execution") 

        # getting the returned value 
        returned_value = func(*args, **kwargs) 
        print("after Execution") 

        # returning the value to the original frame 
        return returned_value 

    return inner1 


# adding decorator to the function 
@hello_decorator
def sum_two_numbers(a, b): 
    print("Inside the function") 
    return a + b 

a, b = 1, 2

# getting the value through return of the function 
print("Sum =", sum_two_numbers(a, b)) 

You can rewrite this code as

def limit_decorator(func): 
    def internal(arg): 

        if (arg >= 0):
            return func(arg) 

        else:
            raise Exception("false input")

    return internal 


@limit_decorator
def square_root(a): 
    return a * 0.5

a = -5

print("Sum =", square_root(a)) 

Answer 2

I would suggest to do the validation of x, using one layer on nested functions (basically merge the validator function into the decorator)

def deco(f):
    def wrapper(x):
        if x<=0:
            return False
        else:
            return f(x)
    return wrapper


@deco
def f(x):
    return x**0.

f(1) #returns false
f(4) #returns 2.0

Answer 3

Try this:

def decorator(validator):
    def subdecorator(function):
        def actual_function(arg):
            if not validator(arg):
                raise ValueError(f"Bad data: {arg}")
            return function(arg)
        return actual_function
    return subdecorator

Answer 4

Here is what you can do

#define decorator...

def validator(x):
    return x>=0

def deco(validator):
    def decorator(func):
        def wrapper_decorator(*args, **kwargs):
            if validator(*args, **kwargs):
                return func(*args, **kwargs)
            else:
                print("error")
                return 
        return wrapper_decorator
    return decorator


@deco(validator)
def f(x):
    return x**0.5

print(f(4)) #should print 2
print(f(-4)) #should print error

The answers everyone has answered are basically correct. However for your case, you require an additional function that acts as a validator. Hence you can add in another outer def to take in the function of the validator and check if it returns True/False.