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Newsgroups: comp.lang.python
Date: Fri, 14 Sep 2012 09:37:37 -0700 (PDT)
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Subject: Re: Decorators not worth the effort
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Xref: csiph.com comp.lang.python:29181

Chris Angelico=E6=96=BC 2012=E5=B9=B49=E6=9C=8814=E6=97=A5=E6=98=9F=E6=9C=
=9F=E4=BA=94UTC+8=E4=B8=8B=E5=8D=8810=E6=99=8241=E5=88=8606=E7=A7=92=E5=AF=
=AB=E9=81=93=EF=BC=9A
> On Sat, Sep 15, 2012 at 12:12 AM, andrea crotti
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> <andrea.crotti.0@gmail.com> wrote:
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> > def fib(n):
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> >     if n <=3D 1:
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> >         return 1
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> >     return fib(n-1) + fib(n-2)
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> >
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> > @memoize
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> > def fib_memoized(n):
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> >     if n <=3D 1:
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> >         return 1
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> >     return fib_memoized(n-1) + fib_memoized(n-2)
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> >
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> >
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> > The second fibonacci looks exactly the same but while the first is
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> > very slow and would generate a stack overflow the second doesn't..
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> Trouble is, you're starting with a pretty poor algorithm. It's easy to
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> improve on what's poor. Memoization can still help, but I would start
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> with a better algorithm, such as:
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>=20
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> def fib(n):
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> 	if n<=3D1: return 1
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> 	a,b=3D1,1
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> 	for i in range(1,n,2):
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> 		a+=3Db
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> 		b+=3Da
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> 	return b if n%2 else a
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>=20
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> def fib(n,cache=3D[1,1]):
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> 	if n<=3D1: return 1
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> 	while len(cache)<=3Dn:
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> 		cache.append(cache[-1] + cache[-2])
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> 	return cache[n]
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> Personally, I don't mind (ab)using default arguments for caching, but
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> you could do the same sort of thing with a decorator if you prefer. I
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> think the non-decorated non-recursive version is clear and efficient
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> though.
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> ChrisA

Uhn, the decorator part is good for wrapping functions in python.

For example a decorator can be used  to add a layor of some
message handlings of  those  plain functions
to become iterators which could be used as call back functions
in a more elegant way.