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Review: Decorators without Arguments

Метки: python

If we create a decorator without arguments, the function to be decorated is passed to the constructor, and the __call__() method is called whenever the decorated function is invoked:

# PythonDecorators/decorator_without_arguments.py
class decorator_without_arguments(object):

    def __init__(self, f):
        """
        If there are no decorator arguments, the function
        to be decorated is passed to the constructor.
        """
        print("Inside __init__()")
        self.f = f

    def __call__(self, *args):
        """
        The __call__ method is not called until the
        decorated function is called.
        """
        print("Inside __call__()")
        self.f(*args)
        print("After self.f(*args)")

@decorator_without_arguments
def sayHello(a1, a2, a3, a4):
    print('sayHello arguments:', a1, a2, a3, a4)

print("After decoration")

print("Preparing to call sayHello()")
sayHello("say", "hello", "argument", "list")
print("After first sayHello() call")
sayHello("a", "different", "set of", "arguments")
print("After second sayHello() call")

Any arguments for the decorated function are just passed to __call__(). The output is:

Inside __init__()
After decoration
Preparing to call sayHello()
Inside __call__()
sayHello arguments: say hello argument list
After self.f(*args)
After first sayHello() call
Inside __call__()
sayHello arguments: a different set of arguments
After self.f(*args)
After second sayHello() call

Notice that __init__() is the only method called to perform decoration, and __call__() is called every time you call the decorated sayHello().