python - 我可以使用函数结果的属性作为装饰器吗？

Question

我用 Python 为自己制作了一个简单的事件系统，我发现每次触发事件的方式几乎都一样:要么在调用结束时，要么在调用之前。感觉这将是一个装饰师的好东西。这是我正在使用的代码:

from functools import wraps

def fires(event):
    """
    Returns a decorater that causes an `Event` to fire immediately before the
    decorated function is called
    """
    def beforeDecorator(f):
        """Fires the event before the function executes"""
        @wraps(f)
        def wrapped(*args, **kargs):
            event.fire(*args, **kargs)
            return f(*args, **kargs)
        return wrapped

    def afterDecorator(f):
        """Fires the event after the function executes"""
        @wraps(f)
        def wrapped(*args, **kargs):
            result = f(*args, **kargs)
            event.fire(*args, **kargs)
            return result
        return wrapped

    # Should allow more explicit `@fires(event).uponCompletion` and
    # `@fires(event).whenCalled`
    afterDecorator.onceComplete = afterDecorator
    afterDecorator.whenCalled = afterDecorator

    return afterDecorator

有了这段代码，我就可以成功地写出:

@fires(myEvent)
def foo(y):
    return y*y

print func(2)

一切正常。当我尝试写这个时，问题就来了:

@fires(myEvent).onceComplete
def foo(y):
    return y*y

print func(2)

这给了我一个语法错误。复杂的装饰器是否有一些特殊的语法？解析器是否在第一组括号后停止？

Answer 1

不，根据 grammar specification ，不可能:

funcdef        ::=  [decorators] "def" funcname "(" [parameter_list] ")" ["->" expression] ":" suitedecorators     ::=  decorator+decorator      ::=  "@" dotted_name ["(" [argument_list [","]] ")"] NEWLINEdotted_name    ::=  identifier ("." identifier)*parameter_list ::=  (defparameter ",")*                    (  "*" [parameter] ("," defparameter)*                    [, "**" parameter]                    | "**" parameter                    | defparameter [","] )parameter      ::=  identifier [":" expression]defparameter   ::=  parameter ["=" expression]funcname       ::=  identifier

装饰器的末尾必须有圆括号