Help- Recursion v. Iter Speed comparison
actuary77
actuary77 at elemental-systems.com
Thu Mar 3 23:19:05 CET 2005
Robert Kern wrote:
> actuary77 wrote:
>
>> #================================================
>> # non-generator
>> #================================================
>>
>>
>> def f1(afunc,aseed,n):
>> values = [afunc(aseed)]
>> for i in range(n-1):
>> values.append(afunc(values[-1]))
>> return values[-1]
>>
>> _b=time()
>> for _i in range(0,100):
>> _y = f1(myfunc,seed,n)
>
>
> Why do you do this? The whole point of this approach was to keep the
> intermediate results instead of recomputing them every time!
>
The point is to get some meaningful results when "timing" the function.
> And why do you prepend underscores everywhere? It's bad Python style.
I prepend underscore to differentiate local,private variables vs. global
variables. Do not want to create a conflict. It is my understanding
that this is the Python style for local v. global variables.
>
>> _e=time()
>> _t=_e-_b
>>
>> print "f1 result: %r time: %f\n" % (_y,_t*10000.)
>>
>>
>> #================================================
>> # generator
>> #================================================
>>
>> def f2(afunc,aseed,n):
>> v = myfunc(aseed)
>> print v
>> for i in range(n):
>> yield v
>> v = afunc(v)
>>
>> def f2gen(i):
>> for _i in range(1,n-1):
>> f2(myfunc,seed,n)
>> return f2(myfunc,seed,n)
>> _b=time()
>> for _i in range(0,cnt):
>> _y = f2gen(_i)
>> _e=time()
>> _t=_e-_b
>> print "f2gen result: %r time: %f\n" % (_y,_t*10000.)
>>
>>
>> ==>
>>
>> rec result: 10.005049999999988 time: 47669.999599
>>
>> f1 result: 10.004999999999988 time: 399.999619
>>
>> f2gen result: <generator object at 0x008D74E0> time: 30739.998817
>>
>> I don't know how to get the generator to work correcly, I understand
>> that the yield preserves the state of the funcion every time it is
>> called. So in order to have myfunc called 50 times, the generator must
>> be called 50 times, but it refuses to return a value. PEP 255 isn't
>> helping me.
>
>
> No, the generator call creates a generator object which you iterate over.
>
> for value in f2(myfunc, seed, n):
> print value
>
> If you absolutely need a list:
>
> list(f2(myfunc, seed, n))
>
Thank you.
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