On Sun, 09 Apr 2006 09:51:18 +0200, Fredrik Lundh wrote:
> Chance Ginger" wrote:
>
>> If I define a decorator like:
>>
>> def t(x) :
>> def I(x) : return x
>> return I
>
> ... you get a syntax error.
>
It isn't a syntax error...I tried it before I posted. In fact
def t(x) :
def I(x) : return x
return I
is correct.
>> and use it like:
>>
>> @t(X)
>> def foo(a) :
>> # definition of foo...
>> pass
>
> that's also a syntax error.
Once again this isn't an error assuming you pass in a valid 'X'.
>
>> or maybe this:
>>
>> @t(X)
>> @(Y)
>> def bar(a) :
>> # The definition of bar...
>
> and that's not even fixable.
>
Again you are mistaken. If I say:
@t(1)
@t(2)
def bar(a) : pass
It is perfectly valid.
>> Will in encounter much of a penalty in executing
>> 'foo' or 'bar'?
>
> since foo is wrapped, calling foo will call your I function, which in
> turn calls the original foo.
>
>> If so, is there a way to define t such that Python knows it is
>> the identity function and short-circuit evaluation?
>
> if you don't want to wrap something, don't wrap it:
>
> def t(x) :
> def I(x) :
> return x
> if date == friday:
> return x # don't wrap it
> return I # wrap it
>
> </F>
Decorators are a way to add "syntactic" sugar to Python,
extending it in ways that make it useful for tools. What
I am trying to do is lessen the impact on the time used
in executing Python code when I use some forms of decorators.
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