Decorators, Identity functions and execution...

[Fredrik Lundh]

Chance Ginger" wrote:

> If I define a decorator like:
>
> def t(x) :
> def I(x) : return x
> return I

... you get a syntax error.

> and use it like:
>
> @t(X)
> def foo(a) :
> # definition of foo...
> pass

that's also a syntax error.

> or maybe this:
>
> @t(X)
> @(Y)
> def bar(a) :
> # The definition of bar...

and that's not even fixable.

> 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>