[Tutor] Writing decorators?

Alan Gauld alan.gauld at yahoo.co.uk
Tue Jul 5 19:06:49 EDT 2016

On 05/07/16 18:31, Alex Hall wrote:

> For decorators, do you never include parentheses except for passing
> arguments? It seems a bit odd to drop them if they'd be empty, given that
> anywhere else doing so would return the function object rather than call
> it. 

Remember what the @ sign is doing.

def func():...

is effectively suyntactic sugar for

func = decorator(func)

If you write @decorator()

That translates to


which is not at all the same thing.

Of course you could get into brain melting mode and
write a meta-decorator that returns a decorator!

>>> def meta():
	def decorator(f):
	    def logit(*args,**kwargs):
		    print("called function with ", args, kwargs)
		    return f(*args,**kwargs)
	    return logit
	return decorator

>>> @meta()    #with parens and potentially args
def square(x): return x*x

>>> square(3)
called function with  (3,) {}

yikes! It all starts to get too complicated for my tiny
brain at this point and I usually find another more
explicit way to do what I need...

Alan G
Author of the Learn to Program web site
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