Re: Need help in understanding a python code
On Sun, 16 Nov 2008 04:34:40 -0800, John Machin wrote: Nothing to do with style. It was the screaming inefficiency of: if non_trivial_condition: return x if not non_trivial_condition: return y that fired me up. Screaming inefficiency? Try micro-optimization. The difference in execution time between if x... if not x... versus if x... else... on my slow, underpowered machine is about 10**-8 seconds. If that's your idea of screaming inefficiency I can't understand why you're programming in Python in the first place. Of course, if x is an expensive function call (say, a network lookup or database query rather than a relatively cheap list indexing operation) then the more readable, Pythonic solution will also be significantly faster. There's no doubt that it should be preferred -- I'm not defending it, as such, just pointing out the over-reaction of dismissing what is a generally well-written and thought-out article on the basis of a triviality. http://en.wikipedia.org/wiki/Style_over_substance_fallacy Quoted Wikipedia - instant disqualification - you lose. Good night. Oh gosh, well, you've certainly proven your case, how could I be so stupid? My apology for thinking that you were acting like an arrogant, bad-tempered dick. I don't know *what* I was thinking. -- Steven who would link to Wikipedia for the definition of sarcasm except I've already lost once in this thread and that's enough. -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
On Nov 16, 4:15 pm, Meryl Silverburgh [EMAIL PROTECTED] wrote: This is the full source code: def A(w, v, i,j): if i == 0 or j == 0: return 0 if w[i-1] j: return A(w, v, i-1, j) if w[i-1] = j: return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) Huh??? There is only a very slight resemblance to the code that you posted previously ... both contain 'max, 'i', and 'j' I am reading this blog http://20bits.com/articles/introduction-to-dynamic-programming/ I suggest that you don't bother reading a blog written by somebody who (presumably consciously) keyed in that if w[i-1] = j: above. Oh, very interesting, it contains: def msum(a): return max([(sum(a[j:i]), (j,i)) for i in range(1,len(a)+1) for j in range(i)]) Would you care to tell us which part of which function you are now trying to understand? -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
On Sun, 16 Nov 2008 01:50:16 -0800, John Machin wrote: def A(w, v, i,j): if i == 0 or j == 0: return 0 if w[i-1] j: return A(w, v, i-1, j) if w[i-1] = j: return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) I am reading this blog http://20bits.com/articles/introduction-to-dynamic-programming/ I suggest that you don't bother reading a blog written by somebody who (presumably consciously) keyed in that if w[i-1] = j: above. That is a translation of standard terminology for a hybrid function. Mathematics doesn't have an else, so you write hybrid functions by enumerating each branch as an if. While it's not especially good Python technique, it's a perfectly idiomatic mathematical expression, and shouldn't be the basis for dismissing an entire blog. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
On Nov 16, 9:31 pm, Steven D'Aprano [EMAIL PROTECTED] cybersource.com.au wrote: On Sun, 16 Nov 2008 01:50:16 -0800, John Machin wrote: def A(w, v, i,j): if i == 0 or j == 0: return 0 if w[i-1] j: return A(w, v, i-1, j) if w[i-1] = j: return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) I am reading this blog http://20bits.com/articles/introduction-to-dynamic-programming/ I suggest that you don't bother reading a blog written by somebody who (presumably consciously) keyed in that if w[i-1] = j: above. That is a translation of standard terminology for a hybrid function. Mathematics doesn't have an else, so you write hybrid functions by enumerating each branch as an if. An else is not required. if w[i-1] j: return A(w, v, i-1, j) return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) While it's not especially good Python technique, it's a perfectly idiomatic mathematical expression, and shouldn't be the basis for dismissing an entire blog. He's meant to be writing Python code, not mathematical expressions. -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
On Sun, 16 Nov 2008 02:41:03 -0800, John Machin wrote: On Nov 16, 9:31 pm, Steven D'Aprano [EMAIL PROTECTED] cybersource.com.au wrote: On Sun, 16 Nov 2008 01:50:16 -0800, John Machin wrote: def A(w, v, i,j): if i == 0 or j == 0: return 0 if w[i-1] j: return A(w, v, i-1, j) if w[i-1] = j: return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) I am reading this blog http://20bits.com/articles/introduction-to-dynamic-programming/ I suggest that you don't bother reading a blog written by somebody who (presumably consciously) keyed in that if w[i-1] = j: above. That is a translation of standard terminology for a hybrid function. Mathematics doesn't have an else, so you write hybrid functions by enumerating each branch as an if. An else is not required. if w[i-1] j: return A(w, v, i-1, j) return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) Which is also not valid terminology for hybrid functions. While it's not especially good Python technique, it's a perfectly idiomatic mathematical expression, and shouldn't be the basis for dismissing an entire blog. He's meant to be writing Python code, not mathematical expressions. And he's written Python code. Perfectly valid Python code. Just because it is not what you consider to be idiomatic Python code isn't a good reason to dismiss his entire blog. What you've done is rather like me saying that because you failed to use a colon after required, and therefore haven't written what *I* consider good English style, not only is your specific post best avoided, but *all* your posts should be avoided. I trust you understand the logical fallacy I would be making, which you have already made. http://en.wikipedia.org/wiki/Style_over_substance_fallacy -- Steven and now begins the arguments as to whether it is a fallacy, and if so, if it is the fallacy I have said it is... -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
On Nov 16, 11:04 pm, Steven D'Aprano [EMAIL PROTECTED] cybersource.com.au wrote: On Sun, 16 Nov 2008 02:41:03 -0800, John Machin wrote: On Nov 16, 9:31 pm, Steven D'Aprano [EMAIL PROTECTED] cybersource.com.au wrote: On Sun, 16 Nov 2008 01:50:16 -0800, John Machin wrote: def A(w, v, i,j): if i == 0 or j == 0: return 0 if w[i-1] j: return A(w, v, i-1, j) if w[i-1] = j: return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) I am reading this blog http://20bits.com/articles/introduction-to-dynamic-programming/ I suggest that you don't bother reading a blog written by somebody who (presumably consciously) keyed in that if w[i-1] = j: above. That is a translation of standard terminology for a hybrid function. Mathematics doesn't have an else, so you write hybrid functions by enumerating each branch as an if. An else is not required. if w[i-1] j: return A(w, v, i-1, j) return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) Which is also not valid terminology for hybrid functions. I couldn't care less. It's valid and efficient (compared to the original) Python. While it's not especially good Python technique, it's a perfectly idiomatic mathematical expression, and shouldn't be the basis for dismissing an entire blog. He's meant to be writing Python code, not mathematical expressions. And he's written Python code. Perfectly valid Python code. Just because it is not what you consider to be idiomatic Python code isn't a good reason to dismiss his entire blog. What you've done is rather like me saying that because you failed to use a colon after required, and therefore haven't written what *I* consider good English style, not only is your specific post best avoided, but *all* your posts should be avoided. I trust you understand the logical fallacy I would be making, which you have already made. Nothing to do with style. It was the screaming inefficiency of: if non_trivial_condition: return x if not non_trivial_condition: return y that fired me up. http://en.wikipedia.org/wiki/Style_over_substance_fallacy Quoted Wikipedia - instant disqualification - you lose. Good night. -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
On Nov 16, 7:34 am, John Machin [EMAIL PROTECTED] wrote: On Nov 16, 11:04 pm, Steven D'Aprano [EMAIL PROTECTED] http://en.wikipedia.org/wiki/Style_over_substance_fallacy Quoted Wikipedia - instant disqualification - you lose. Good night. When quoting wikipedia became the new Godwin's law ?? :) George -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
On Nov 17, 5:26 am, George Sakkis [EMAIL PROTECTED] wrote: When quoting wikipedia became the new Godwin's law ?? :) Probably at the point the editors started becoming revisionists and culling anything they didn't consider notable enough. -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
On Sun, Nov 16, 2008 at 7:34 AM, John Machin [EMAIL PROTECTED] wrote: On Nov 16, 11:04 pm, Steven D'Aprano [EMAIL PROTECTED] cybersource.com.au wrote: On Sun, 16 Nov 2008 02:41:03 -0800, John Machin wrote: On Nov 16, 9:31 pm, Steven D'Aprano [EMAIL PROTECTED] cybersource.com.au wrote: On Sun, 16 Nov 2008 01:50:16 -0800, John Machin wrote: def A(w, v, i,j): if i == 0 or j == 0: return 0 if w[i-1] j: return A(w, v, i-1, j) if w[i-1] = j: return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) I am reading this blog http://20bits.com/articles/introduction-to-dynamic-programming/ I suggest that you don't bother reading a blog written by somebody who (presumably consciously) keyed in that if w[i-1] = j: above. That is a translation of standard terminology for a hybrid function. Mathematics doesn't have an else, so you write hybrid functions by enumerating each branch as an if. An else is not required. if w[i-1] j: return A(w, v, i-1, j) return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) Which is also not valid terminology for hybrid functions. I couldn't care less. It's valid and efficient (compared to the original) Python. While it's not especially good Python technique, it's a perfectly idiomatic mathematical expression, and shouldn't be the basis for dismissing an entire blog. He's meant to be writing Python code, not mathematical expressions. And he's written Python code. Perfectly valid Python code. Just because it is not what you consider to be idiomatic Python code isn't a good reason to dismiss his entire blog. What you've done is rather like me saying that because you failed to use a colon after required, and therefore haven't written what *I* consider good English style, not only is your specific post best avoided, but *all* your posts should be avoided. I trust you understand the logical fallacy I would be making, which you have already made. Nothing to do with style. It was the screaming inefficiency of: if non_trivial_condition: return x if not non_trivial_condition: return y that fired me up. http://en.wikipedia.org/wiki/Style_over_substance_fallacy Quoted Wikipedia - instant disqualification - you lose. Good night. If you really believe that, you haven't been following this list long enough. Every terminology dispute always includes at least 1 Wikipedia link. Also, you might want to look at this study: http://news.cnet.com/2100-1038_3-5997332.html -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
Benjamin Kaplan wrote: If you really believe that, you haven't been following this list long enough. Every terminology dispute always includes at least 1 Wikipedia link. Also, you might want to look at this study: http://news.cnet.com/2100-1038_3-5997332.html That study has been disputed; see the links at the top of http://en.wikipedia.org/wiki/Reliability_of_Wikipedia. /me ducks -- -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
On Nov 17, 11:40 am, Matt Nordhoff [EMAIL PROTECTED] wrote: That study has been disputed; see the links at the top of http://en.wikipedia.org/wiki/Reliability_of_Wikipedia. Now, if there was any independent refutation of the original study that isn't based on Britannica's - not that I'm outright accusing them of any bias here :) - that might make a reasonable disputation... -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
On Sat, Nov 15, 2008 at 8:41 PM, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: Hi, I am trying to understand the following line: # a is an integer array max([(sum(a[j:i]), (j,i)) This code isn't valid. You have a [ with no closing ]. Cheers, Chris -- Follow the path of the Iguana... http://rebertia.com Can you please tell me what that means, I think sum(a[j:i] means find the some from a[j] to a[i] But what is the meaning of the part (j,i)? -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
On Nov 16, 3:41 pm, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: Hi, I am trying to understand the following line: # a is an integer array max([(sum(a[j:i]), (j,i)) Can you please tell me what that means, I think sum(a[j:i] means find the some from a[j] to a[i] But what is the meaning of the part (j,i)? 0. integer array is a very loose term in Python. Fortunately the answer to your question is not affected by that. 1. Sorry, the max... line is not syntactically correct; there are two [s and only one ]; there are 4 (s and only 3 )s. Try copying the line and pasting, not re-typing. 2. I'm not going to try to guess how to fix the bracket mismatches. 3. Note that you have left off a ) from your question about sum ... it probably should be sum([j:i]). 4. That is the sum (not some!!) of a[j] to a[i-1] both inclusive. It's a standard idiom in Python for the end of a range to be expressed as the first unused element. 5. Even after fixing the bracket mismatches, it looks like you will have an expression whose value is thrown away. Perhaps you might like to give us a few lines of context before and after the line of interest. -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
This is the full source code: def A(w, v, i,j): if i == 0 or j == 0: return 0 if w[i-1] j: return A(w, v, i-1, j) if w[i-1] = j: return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) I am reading this blog http://20bits.com/articles/introduction-to-dynamic-programming/ On Sat, Nov 15, 2008 at 10:54 PM, Chris Rebert [EMAIL PROTECTED] wrote: On Sat, Nov 15, 2008 at 8:41 PM, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: Hi, I am trying to understand the following line: # a is an integer array max([(sum(a[j:i]), (j,i)) This code isn't valid. You have a [ with no closing ]. Cheers, Chris -- Follow the path of the Iguana... http://rebertia.com Can you please tell me what that means, I think sum(a[j:i] means find the some from a[j] to a[i] But what is the meaning of the part (j,i)? -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
See below. On Nov 15, 11:15 pm, Meryl Silverburgh [EMAIL PROTECTED] wrote: This is the full source code: def A(w, v, i,j): if i == 0 or j == 0: return 0 if w[i-1] j: return A(w, v, i-1, j) if w[i-1] = j: return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) I am reading this blog http://20bits.com/articles/introduction-to-dynamic-programming/ On Sat, Nov 15, 2008 at 10:54 PM, Chris Rebert [EMAIL PROTECTED] wrote: On Sat, Nov 15, 2008 at 8:41 PM, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: Hi, I am trying to understand the following line: # a is an integer array max([(sum(a[j:i]), (j,i)) This code isn't valid. You have a [ with no closing ]. Cheers, Chris -- Follow the path of the Iguana... http://rebertia.com Can you please tell me what that means, I think sum(a[j:i] means find the some from a[j] to a[i] But what is the meaning of the part (j,i)? -- http://mail.python.org/mailman/listinfo/python-list if w[i-1] = j: return max(A(w,v, i-1, j), v[i-1] + A(w,v, i-1, j - w[i-1])) This means: Calculate 'A(w,v, i-1, j)', calculate 'v[i-1] + A(w,v, i-1, j - w [i-1])', and return whichever is larger. -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help in understanding a python code
silverburgh: max([(sum(a[j:i]), (j,i)) Other people have already answered you so I'll add only a small note: today the max() function has a key optional attribute, so that code can also be written as: max(((j, i) for ...), key=lambda (j, i): sum(a[j : i])) I think you have copied that part from code that runs in O(n^2); remember that you can find the max subarray with a well known O(n) algorithm too. Bye, bearophile -- http://mail.python.org/mailman/listinfo/python-list
