Re: how many nested for can we utilize?
Fredrik Lundh
> when I use 20 for ,"SystemError: too many statically nested blocks"
> When I use 100 for ,"IndentationError: too many levels of indentation"
> How to handle these errors?
so why exactly are you trying to nest 20 or 100 for-in loops?
</F>
Nick Dumas
Hash: SHA1
A good quote I read (I can't remember who it was from, though) is "If
you need more than three levels of indentation, then something is
seriously wrong with your code." Possibly Guido himself? Anyway. If
you've got 100 levels of for, you're probably making things way harder
than they need to be.
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Fredrik Lundh
> A good quote I read (I can't remember who it was from, though) is "If
> you need more than three levels of indentation, then something is
> seriously wrong with your code." Possibly Guido himself? Anyway. If
> you've got 100 levels of for, you're probably making things way harder
> than they need to be.
assuming 100 levels of for and 2 items in each sequence, you'll end up
with 1267650600228229401496703205376 iterations through the inner loop.
assuming each iteration takes a picosecond, it'll take approx 40
billion years to run the program.
</F>
Wojtek Walczak
I guess that's exactly why the OP asks the question. He just wants
to start as soon as possible ;-)
--
Regards,
Wojtek Walczak,
http://www.stud.umk.pl/~wojtekwa/
Fredrik Lundh
>> it'll take approx 40 billion years to run the program.
>
> I guess that's exactly why the OP asks the question. He just wants
> to start as soon as possible ;-)
required reading:
"The Effects of Moore's Law and Slacking on Large Computations"
http://arxiv.org/abs/astro-ph/9912202
</F>
Paul Boddie
>
> required reading:
>
> "The Effects of Moore's Law and Slacking on Large Computations"
> http://arxiv.org/abs/astro-ph/9912202
Or maybe this...?
http://docs.python.org/tut/node6.html#SECTION006600000000000000000
And this:
http://www.freenetpages.co.uk/hp/alan.gauld/tutrecur.htm
Paul
Wojtek Walczak
Kinda buddhist approach. Anyway, it might work out, unless the number
of for loops is increasing in time and in 18 months it may be - let's
say - 20 nested for loops more ;) Got to ask the OP.
Fredrik Lundh
>> required reading:
>>
>> "The Effects of Moore's Law and Slacking on Large Computations"
>> http://arxiv.org/abs/astro-ph/9912202
>
> Or maybe this...?
>
> http://docs.python.org/tut/node6.html#SECTION006600000000000000000
and functions will solve the 40-billion year computation problem exactly
how?
</F>
Paul Boddie
>
> and functions will solve the 40-billion year computation problem exactly
> how?
I was thinking more about the need to nest "for" statements to a depth
of 20 levels, which I imagine only arises on a "just in case" basis
for the inquirer. In other words, the inquirer may have input that
could theoretically demand twenty levels of state, each level provided
by a single "for" statement, but in practice they might only need to
manage a few levels of state.
In any case, we're potentially seeing the use of the wrong tool for
the job, and I am speculating that functions would be the right tool,
but unless the inquirer is willing to show the code (which I haven't
seen in this thread yet), it's hard to speculate further.
Paul
Roel Schroeven
> A good quote I read (I can't remember who it was from, though) is "If
> you need more than three levels of indentation, then something is
> seriously wrong with your code." Possibly Guido himself?
Linus Torvalds in the Linux kernel coding style document:
"[...] The answer to that is that if you need more than 3 levels of
indentation, you're screwed anyway, and should fix your program."
(http://lxr.linux.no/linux/Documentation/CodingStyle)
--
The saddest aspect of life right now is that science gathers knowledge
faster than society gathers wisdom.
-- Isaac Asimov
Roel Schroeven
Gabriel Genellina
> Of course We needn't 100 levels,but I use the exec function can concise the
> code. See the attachment.
Just a note on the attached code:
def isPro52Num(n):
s=[]
for i in range(1,7):
s.append(str(i*n))
for i in s[0]:
ll = len(string.join(string.split(s[0],i),''))
for j in range(1,6):
if ll!=len(string.join(string.split(s[j],i),'')):
return False
return True
The functions in the string module have been deprecated ages ago in favor of the corresponding string methods.
In this expression: len(string.join(string.split(s[0],i),'')) if you want to get "the number of digits in s[0] that are not i" I think it's way faster (and more clear) to do len(s[0])-s[0].count(i) instead of creating two lists just to throw them away.
--
Gabriel Genellina
Lie
I think most (all?) algorithm that might use 20+ levels of for-in
loops could almost always be replaced with a recursive function. Or at
least they could be broken into smaller functions.
Reedick, Andrew
Recursion is slow. There was a thread on permutations and I ran some timings on various methods of nesting loops. Also, I do remember hitting nested for limits very quickly. I think list comprehensions allowed for deeper nesting than straight for loops. Anyway, the thread contains various code and solutions that should help the OP.
http://mail.python.org/pipermail/python-list/2008-January/473787.html
Cookbook is relatively decent. 5 deep, 100 iterations:
list comprehension: 11.02
nested for loop : 13.16 +19%
cookbook : 18.85 +71%
recursion : 69.00 +526%
eval : 13.30 +20%
Start of thread: http://mail.python.org/pipermail/python-list/2008-January/473650.html
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