[Tutor] Tutor Digest, Vol 81, Issue 39

Wed Nov 10 21:50:54 CET 2010

"marupalli charan" <marupalli.charan at gmail.com> wrote

> Thanks, but first one not working!!!

First one of what?

Please edit the message to pprovide some context
and pay attention to the instruxctions that you so helpfully
posted:

>> When replying, please edit your Subject line so it is more specific
>> than "Re: Contents of Tutor digest..."
>>
>>
>> Today's Topics:
>>
>>    1. Re: List comprehension question (Richard D. Moores)
>>    2. Re: query result set (bob gailer)
>>    3. Re: Columnar Transposition Cipher question (Stefan Behnel)
>>    4. Re: Columnar Transposition Cipher question (Eike Welk)
>>    5. Re: List comprehension question (Steven D'Aprano)
>>    6. Re: Columnar Transposition Cipher question (Steven D'Aprano)
>>    7. Re: List comprehension question (Albert-Jan Roskam)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Tue, 9 Nov 2010 08:17:55 -0800
>> From: "Richard D. Moores" <rdmoores at gmail.com>
>> To: "Martin A. Brown" <martin at linux-ip.net>
>> Cc: tutor at python.org
>> Subject: Re: [Tutor] List comprehension question
>> Message-ID:
>> <AANLkTi=-=zYvQA7z6H6fNg3MGonJCL9BrCJxJ3_fFZfv at mail.gmail.com>
>> Content-Type: text/plain; charset=UTF-8
>>
>> On Tue, Nov 9, 2010 at 05:51, Martin A. Brown <martin at linux-ip.net> 
>> wrote:
>>>
>>> Hello,
>>>
>>> ?: def proper_divisors_sum(n):
>>> ?: ? ? pd_list = []
>>> ?: ? ? for x in range(1, int(n**.5)+1):
>>> ?: ? ? ? ? if n % x == 0:
>>> ?: ? ? ? ? ? ? factor = int(x)
>>> ?: ? ? ? ? ? ? pd_list.append(factor)
>>> ?: ? ? ? ? ? ? factor2 = int(n/factor)
>>> ?: ? ? ? ? ? ? pd_list.append(factor2)
>>> ?: ? ? pd_list = list(set(pd_list))
>>> ?: ? ? pd_list.sort()
>>> ?: ? ? pd_list = pd_list[:-1]
>>> ?: ? ? return sum(pd_list)
>>>
>>> A few questions--noting, of course, that I'm not reading this with
>>> an eye toward performance, which it seems you are, but these occur
>>> to me:
>>>
>>> ?* Why use a list (pd_list = []), when you want unique divisors?
>>> ? ?Why not, pd = set() ? ?Then, instead of pd_list.append(factor),
>>> ? ?pd.add(factor) or something like pd.update((factor,factor2))?
>>> ? ?(See also my suggestion below.)
>>>
>>> ?* Also, since you are throwing away the divisor n, anyway,
>>> ? ?why not skip it from the beginning? ?Like this:
>>>
>>> ? ? ?pd_list = [1,]
>>> ? ? ?for x in range(2, int(n**.5)+1):
>>>
>>> ?* So, I'm not terribly math aware, but I don't think I have
>>> ? ?substantially changed the meaning of your program. ?I find
>>> ? ?breaking out the functions makes things a bit clearer to
>>> ? ?somebody who might be reading my code later.
>>>
>>> Combining these suggestions and splitting into separate functions
>>> (you don't really need to sort before summing), I end up with the
>>> below. ?Note, that I stuff the proper divisor 1 in the set at
>>> creation time. ?This is probably not worth it from an optimization
>>> perspective, but as I have learned, the only way to know is to 
>>> time
>>> it (and I didn't time it).
>>>
>>> ? ? ?def proper_divisors_sum(n):
>>> ? ? ? ? ?return sum(proper_divisors(n))
>>>
>>> ? ? ?def proper_divisors_sorted(n):
>>> ? ? ? ? ?return sorted(proper_divisors(n))
>>>
>>> ? ? ?def proper_divisors(n):
>>> ? ? ? ? ?pd = set((1,))
>>> ? ? ? ? ?for x in range(2, int(n**.5)+1):
>>> ? ? ? ? ? ? ?factor, mod = divmod(n,x)
>>> ? ? ? ? ? ? ?if mod == 0:
>>> ? ? ? ? ? ? ? ? ?pd.update((x,factor))
>>> ? ? ? ? ?return list(pd)
>>
>> Thanks for your ideas, Martin. I adopted your idea of starting at 
>> 2,
>> with an initial list of [1].  It resulted in a small increase in
>> speed. And you're right, I don't need to sort.
>>
>> Speed is important, because the function is the heart of my amiable
>> numbers script. Did you happen to see that post of mine?
>>
>> #Here's my fastest version before seeing Martin's post:
>> def proper_divisors_sum1(n):
>>     pd_list = []
>>     for x in range(1, int(n**.5)+1):
>>         if n % x == 0:
>>             pd_list.append(x)
>>             pd_list.append(n//x)
>>     pd_list = list(set(pd_list))
>>     pd_list.sort()
>>     pd_list = pd_list[:-1]
>>     return sum(pd_list)
>>
>> #This uses several of Martin's ideas
>> # It's now my fastest version
>> def proper_divisors_sum2(n):
>>     pd = set((1,))
>>     for x in range(2, int(n**.5)+1):
>>         if n % x == 0:
>>             pd.update((x, n//x))
>>     return sum(list(pd))
>>
>> Here's what I put together from all your points, except for the
>> splitting off of several small functions:
>>
>> # This incorporates all of Martin's ideas
>> # Seems that divmod() is a speed killer
>> def proper_divisors_sum3(n):
>>     pd = set((1,))
>>     for x in range(2, int(n**.5)+1):
>>         factor, mod = divmod(n,x)
>>         if mod == 0:
>>             pd.update((x,factor))
>>     return sum(list(pd))
>>
>> It may be that I've haven't done your suggestions justice, but that
>> function is 76% slower than proper_divisors_sum2().
>>
>> See <http://tutoree7.pastebin.com/R82876Eg> for a speed test with n 
>> =
>> 100,000 and 100,000 loops
>>
>> Thanks again, Martin.
>>
>> Dick
>>
>>
>> ------------------------------
>>
>> Message: 2
>> Date: Tue, 09 Nov 2010 12:00:56 -0500
>> From: bob gailer <bgailer at gmail.com>
>> To: tutor at python.org
>> Subject: Re: [Tutor] query result set
>> Message-ID: <4CD97E48.9080604 at gmail.com>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>> When starting a new subject, please start with a new email. Do not
>> "hijack" an existing one, as that causes your query to appear as 
>> part of
>> the hijacked thread.
>>
>>
>> --
>> Bob Gailer
>> 919-636-4239
>> Chapel Hill NC
>>
>>
>>
>> ------------------------------
>>
>> Message: 3
>> Date: Tue, 09 Nov 2010 18:36:43 +0100
>> From: Stefan Behnel <stefan_ml at behnel.de>
>> To: tutor at python.org
>> Subject: Re: [Tutor] Columnar Transposition Cipher question
>> Message-ID: <ibc0rb$g96$1 at dough.gmane.org>
>> Content-Type: text/plain; charset=UTF-8; format=flowed
>>
>> Steven D'Aprano, 09.11.2010 05:01:
>>> http://pypi.python.org/pypi/obfuscate
>>
>> Hmm - why is the Windows installer on that page called 
>> "linux-i686"?
>>
>> Stefan
>>
>>
>>
>> ------------------------------
>>
>> Message: 4
>> Date: Tue, 9 Nov 2010 19:37:28 +0100
>> From: Eike Welk <eike.welk at gmx.net>
>> To: tutor at python.org
>> Subject: Re: [Tutor] Columnar Transposition Cipher question
>> Message-ID: <201011091937.28881.eike.welk at gmx.net>
>> Content-Type: Text/Plain;  charset="iso-8859-1"
>>
>> On Tuesday 09.11.2010 18:36:43 Stefan Behnel wrote:
>>> Steven D'Aprano, 09.11.2010 05:01:
>>> > http://pypi.python.org/pypi/obfuscate
>>>
>>> Hmm - why is the Windows installer on that page called 
>>> "linux-i686"?
>>
>> It was probably created on Linux. Python's Distutils create 
>> installers for
>> Windows even on Linux. They get file names that contain "linux-". 
>> You must
>> rename them, otherwise your users get confused.
>>
>> I did never try them, because I have no Windows computer. Do these 
>> Windows
>> installers work when they are created on Linux?
>>
>>
>> Eike.
>>
>>
>> ------------------------------
>>
>> Message: 5
>> Date: Wed, 10 Nov 2010 07:54:24 +1100
>> From: Steven D'Aprano <steve at pearwood.info>
>> To: tutor at python.org
>> Subject: Re: [Tutor] List comprehension question
>> Message-ID: <4CD9B500.4090605 at pearwood.info>
>> Content-Type: text/plain; charset=UTF-8; format=flowed
>>
>> Richard D. Moores wrote:
>>
>>> See <http://tutoree7.pastebin.com/R82876Eg> for a speed test with 
>>> n =
>>> 100,000 and 100,000 loops
>>
>> As a general rule, you shouldn't try to roll your own speed tests. 
>> There
>> are various subtleties that can throw your results right out. 
>> Timing
>> small code snippets on modern multi-tasking computers is fraught 
>> with
>> difficulties.
>>
>> Fortunately Python comes with that battery already included: the 
>> timeit
>> module. You can use it from the shell like this:
>>
>> python -m timeit -s "setup code goes here" "test code goes here"
>>
>> At the Python interactive interpreter, the most useful pattern I've
>> found is:
>>
>> from timeit import Timer
>> t = Timer("proper_divisors(n)",
>>      "from __main__ import proper_divisors; n = 100000")
>> min(t.repeat(repeat=5, number=100000))
>>
>>
>> Or if you're happy with Python's defaults, that last line can be 
>> just:
>>
>> min(t.repeat())
>>
>>
>>
>> --
>> Steven
>>
>>
>> ------------------------------
>>
>> Message: 6
>> Date: Wed, 10 Nov 2010 08:29:51 +1100
>> From: Steven D'Aprano <steve at pearwood.info>
>> To: tutor at python.org
>> Subject: Re: [Tutor] Columnar Transposition Cipher question
>> Message-ID: <4CD9BD4F.3000309 at pearwood.info>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>> Eike Welk wrote:
>>> On Tuesday 09.11.2010 18:36:43 Stefan Behnel wrote:
>>>> Steven D'Aprano, 09.11.2010 05:01:
>>>>> http://pypi.python.org/pypi/obfuscate
>>>> Hmm - why is the Windows installer on that page called 
>>>> "linux-i686"?
>>>
>>> It was probably created on Linux.
>>
>> That would be it.
>>
>>  > Python's Distutils create installers for
>>> Windows even on Linux. They get file names that contain "linux-". 
>>> You must
>>>
>>> rename them, otherwise your users get confused.
>>
>> I didn't realise that.
>>
>>> I did never try them, because I have no Windows computer. Do these 
>>> Windows
>>>
>>> installers work when they are created on Linux?
>>
>> I'm pretty sure I tried it, once, but I might be confabulating.
>>
>>
>>
>> --
>> Steven
>>
>>
>>
>> ------------------------------
>>
>> Message: 7
>> Date: Tue, 9 Nov 2010 13:58:22 -0800 (PST)
>> From: Albert-Jan Roskam <fomcl at yahoo.com>
>> To: Steven D'Aprano <steve at pearwood.info>, tutor at python.org
>> Subject: Re: [Tutor] List comprehension question
>> Message-ID: <968733.36678.qm at web110711.mail.gq1.yahoo.com>
>> Content-Type: text/plain; charset="us-ascii"
>>
>> For larger blocks of code, cProfile may also be useful for speed 
>> tests.
>>
>>  Cheers!!
>> Albert-Jan
>>
>>
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> All right, but apart from the sanitation, the medicine, education, 
>> wine,
>> public
>> order, irrigation, roads, a fresh water system, and public health, 
>> what have
>> the
>> Romans ever done for us?
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>>
>>
>>
>> ________________________________
>> From: Steven D'Aprano <steve at pearwood.info>
>> To: tutor at python.org
>> Sent: Tue, November 9, 2010 9:54:24 PM
>> Subject: Re: [Tutor] List comprehension question
>>
>> Richard D. Moores wrote:
>>
>>> See <http://tutoree7.pastebin.com/R82876Eg> for a speed test with 
>>> n =
>>> 100,000 and 100,000 loops
>>
>> As a general rule, you shouldn't try to roll your own speed tests. 
>> There are
>> various subtleties that can throw your results right out. Timing 
>> small code
>> snippets on modern multi-tasking computers is fraught with 
>> difficulties.
>>
>> Fortunately Python comes with that battery already included: the 
>> timeit
>> module.
>> You can use it from the shell like this:
>>
>> python -m timeit -s "setup code goes here" "test code goes here"
>>
>> At the Python interactive interpreter, the most useful pattern I've 
>> found
>> is:
>>
>> from timeit import Timer
>> t = Timer("proper_divisors(n)",
>>     "from __main__ import proper_divisors; n = 100000")
>> min(t.repeat(repeat=5, number=100000))
>>
>>
>> Or if you're happy with Python's defaults, that last line can be 
>> just:
>>
>> min(t.repeat())
>>
>>
>>
>> -- Steven
>> _______________________________________________
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>>
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>>
>> End of Tutor Digest, Vol 81, Issue 39
>> *************************************
>>
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