stacked decorators and consolidating
Peter Otten
__peter__ at web.de
Tue Oct 29 13:52:19 EDT 2013
Tim Chase wrote:
> I've got some decorators that work fine as such:
>
> @dec1(args1)
> @dec2(args2)
> @dec3(args3)
> def myfun(...):
> pass
>
> However, I used that sequence quite a bit, so I figured I could do
> something like
>
> dec_all = dec1(args1)(dec2(args2)(dec3(args3)))
With these shortcuts
a = dec1(args1)
b = dec2(args2)
c = dec3(args3)
to make it look less messy your first attempt is
dec_all = a(b(c))
and the final decorated function will be
a(b(c))(myfun)
when it should be
a(b(c(myfun)))
i. e. instead of decorating myfun three times you are decorating the
decorator c twice and then use the result of that decoration to decorate
myfunc.
Does that help? I have my doubts ;)
> to consolidate the whole mess down to
>
> @dec_all
> def myfun(...):
> pass
>
> However, this yields different (test-breaking) results. Messing
> around, I found that if I write it as
>
> dec_all = lambda fn: dec1(args1)(dec2(args2)(dec3(args3)(fn)))
>
> it works and passes all preexisting tests.
>
> What am I missing that would cause this difference in behavior?
>
> -tkc
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