Re: Python without a tty
On Sep 29, 3:52 am, Steven D'Aprano steve +comp.lang.pyt...@pearwood.info wrote: Alain Ketterlin wrote: Steven D'Aprano steve+comp.lang.pyt...@pearwood.info writes: I have a Python script which I would like to test without a tty attached to the process. I could run it as a cron job, but is there an easier way? I am running Linux. Isn't os.setsid() what you're looking for? It makes the calling process have no controlling terminal. There's also a user command called setsid that should have the same effect. It doesn't appear so to me. [steve@sylar ~]$ tty /dev/pts/16 [steve@sylar ~]$ setsid tty /dev/pts/16 [steve@sylar ~]$ python -c import sys,os; print os.isatty(sys.stdout.fileno()) True [steve@sylar ~]$ setsid python -c import sys,os; print os.isatty(sys.stdout.fileno()) True If I run the same Python command (without the setsid) as a cron job, I get False emailed to me. That's the effect I'm looking for. -- Steven You could try the old UNIX nohup ... technique for running a process in the background (the ) with no HangUP if you log out: $ nohup python -c import sys,os; print os.isatty(sys.stdout.fileno()) appending output to nohup.out $ cat nohup.out False But that is over kill I guess. One worrying detail the definition of a running process in UNIX implies is that it has standard input/output files open. You'd be wise to make sure that they are connected to things that are safe /dev/null. Even so /dev/tty can be opened any way... Hope this helps. -- http://mail.python.org/mailman/listinfo/python-list
Re: Faster Recursive Fibonacci Numbers
On May 17, 9:36 am, rusi rustompm...@gmail.com wrote: On May 17, 8:50 pm, RJB rbott...@csusb.edu wrote: I noticed some discussion of recursion. the trick is to find a formula where the arguments are divided, not decremented. I've had a divide-and-conquer recursion for the Fibonacci numbers for a couple of years in C++ but just for fun rewrote it in Python. It was easy. Enjoy. And tell me how I can improve it! def fibo(n): A Faster recursive Fibonaci function Use a formula from Knuth Vol 1 page 80, section 1.2.8: If F[n] is the n'th Fibonaci number then F[n+m] = F[m]*F[n+1] + F[m-1]*F[n]. First set m = n+1 F[ 2*n+1 ] = F[n+1]**2 + F[n]*2. Then put m = n in Knuth's formula, F[ 2*n ] = F[n]*F[n+1] + F[n-1]* F[n], and replace F[n+1] by F[n]+F[n-1], F[ 2*n ] = F[n]*(F[n] + 2*F[n-1]). if n=0: return 0 elif n=2: return 1 elif n%2==0: half=n//2 f1=fibo(half) f2=fibo(half-1) return f1*(f1+2*f2) else: nearhalf=(n-1)//2 f1=fibo(nearhalf+1) f2=fibo(nearhalf) return f1*f1 + f2*f2 RJB the Lurkerhttp://www.csci.csusb.edu/dick/cs320/lab/10.html - Its an interesting problem and you are 75% there. You see the halving gives you logarithmic behavior and the double calls give exponential behavior. So how to get rid of double calls? Its quite simple: Just define your function in terms of return pairs of adjacent pairs ie (fib(n), fib(n +1)) for some n rather then a single number fib(n) Here's a straightforward linear function: def fp(n): #fibpair if n==1: return (1,1) else: a,b = fp(n-1) return (b, a+b) def fib(n): a,b = fp(n) return a --- Now use this (pairing) idea with your (halving) identities and you should get a logarithmic algo. [If you cant do it ask again but yes its fun to work out so do try :-) ] Thank you! Very cool and clear. I hoped that there was something that Python made natural I couldn't see after 50 years in other languages. I'd like to work on combining both approaches. It may take a while... -- http://mail.python.org/mailman/listinfo/python-list
Faster Recursive Fibonacci Numbers
I noticed some discussion of recursion. the trick is to find a formula where the arguments are divided, not decremented. I've had a divide-and-conquer recursion for the Fibonacci numbers for a couple of years in C++ but just for fun rewrote it in Python. It was easy. Enjoy. And tell me how I can improve it! def fibo(n): A Faster recursive Fibonaci function Use a formula from Knuth Vol 1 page 80, section 1.2.8: If F[n] is the n'th Fibonaci number then F[n+m] = F[m]*F[n+1] + F[m-1]*F[n]. First set m = n+1 F[ 2*n+1 ] = F[n+1]**2 + F[n]*2. Then put m = n in Knuth's formula, F[ 2*n ] = F[n]*F[n+1] + F[n-1]* F[n], and replace F[n+1] by F[n]+F[n-1], F[ 2*n ] = F[n]*(F[n] + 2*F[n-1]). if n=0: return 0 elif n=2: return 1 elif n%2==0: half=n//2 f1=fibo(half) f2=fibo(half-1) return f1*(f1+2*f2) else: nearhalf=(n-1)//2 f1=fibo(nearhalf+1) f2=fibo(nearhalf) return f1*f1 + f2*f2 RJB the Lurker http://www.csci.csusb.edu/dick/cs320/lab/10.html -- http://mail.python.org/mailman/listinfo/python-list
Re: Vectors
On Apr 20, 6:43 am, Andreas Tawn andreas.t...@ubisoft.com wrote: Algis Kabaila akaba...@pcug.org.au writes: Are there any modules for vector algebra (three dimensional vectors, vector addition, subtraction, multiplication [scalar and vector]. Could you give me a reference to such module? NumPy has array (and matrix) types with support for these basic operations you mention. See the tutorial athttp://numpy.scipy.org/ You might also want to considerhttp://code.google.com/p/pyeuclid/ Cheers, Drea Pyeuclid docs don't mention dot or cross products. RJB -- http://mail.python.org/mailman/listinfo/python-list
Re: Another related OO Python ?
On Feb 16, 6:21 am, Eric Brunel eric.bru...@pragmadev.nospam.com wrote: In article 6849fd3f-5116-4b35-b274-dc76ae39f...@a11g2000pro.googlegroups.com, RJB rbott...@csusb.edu wrote: On Feb 16, 12:48 am, Eric Brunel eric.bru...@pragmadev.nospam.com wrote: In article iJg5p.198317$mg5.147...@en-nntp-06.dc1.easynews.com, Doug Epling wde...@mikrotec.com wrote: hey, does anyone find the UML useful during Python development of larger projects? Well, UML being very Java/C++ oriented, I found out that Python idioms were really difficult to represent in the diagrams. So I'm using it to a very small extent and for documentation only, just to give an idea about how classes are organized. For the rest, and IMHO, it's really too impractical to be of any use. Which of the 13 diagrams have tried and rejected?-) Diagrams that aren't too bound to the language like e.g the deployment diagram can still be used, of course. I was mainly talking about the class diagram, which is still the central point of a model. But I even found sequence diagrams quite hard to write for Python, unless they are very simplistic ones. Yes. Especially if you draw interactions with a tool and make them tidy. I believe in very rough and rapid sketches in pencil or chalk. Complex code either needs rethinking or in the worst case an activity diagram, IMHO. Of course doing the diagrams by hand after the code is OK How do you justify the time spent doing it? -- http://mail.python.org/mailman/listinfo/python-list
Re: Another related OO Python ?
On Feb 16, 12:48 am, Eric Brunel eric.bru...@pragmadev.nospam.com wrote: In article iJg5p.198317$mg5.147...@en-nntp-06.dc1.easynews.com, Doug Epling wde...@mikrotec.com wrote: hey, does anyone find the UML useful during Python development of larger projects? Well, UML being very Java/C++ oriented, I found out that Python idioms were really difficult to represent in the diagrams. So I'm using it to a very small extent and for documentation only, just to give an idea about how classes are organized. For the rest, and IMHO, it's really too impractical to be of any use. Which of the 13 diagrams have tried and rejected?-) -- http://mail.python.org/mailman/listinfo/python-list
Re: Easy function, please help.
On Feb 8, 11:08 pm, Paul Rudin paul.nos...@rudin.co.uk wrote: It works because 0 tests false and because integer division yields integers... eventually you'll get something like 1/10 giving 0. It's not necessarily a good thing to rely on. For example if you try it after from __future__ import division - or in python 3 - you'll get a float as the result of the division and it won't test False. What operator should I use if I want integer division? Ada and Pascal used div if I recall rightly. -- http://mail.python.org/mailman/listinfo/python-list
Re: what's the precision of fractions.Fraction?
Does Fractions remove common factors the way it should? If it does and you want to find the closest fraction with a smaller denominator i think tou'll need some number theory and continued fractions. RJB On Nov 18, 8:26 pm, Steven D'Aprano st...@remove-this- cybersource.com.au wrote: On Thu, 18 Nov 2010 20:08:00 +0100, Stefan Sonnenberg-Carstens wrote: If you need it really *precise*, cast your Fractions into type Decimal: It's actually the opposite. Decimal has many advantages, but being really precise is not one of them. It suffers the exact same issues re precision and round-off as binary floating point. It is easy to demonstrate that there are numbers which cannot be represented precisely as Decimals no matter how many decimal places you use, but can be represented exactly as Fractions. Fraction can exactly represent every Decimal, but Decimal cannot represent exactly every Fraction. We're not talking about weird edge cases either, but simple numbers that you're likely to come across every day: from decimal import Decimal one_ninth = Decimal(1)/Decimal(9) two_thirds = Decimal(2)/Decimal(3) one_ninth*6 == two_thirds False from fractions import Fraction one_ninth = Fraction(1, 9) two_thirds = Fraction(2, 3) one_ninth*6 == two_thirds True Still not convinced? f = Fraction(1) + Fraction(1, 10**10) f != 1 True (which is virtually instantaneous, by the way) compared to the *much* slower: d = Decimal(1) + Decimal(1)/Decimal(10**10) d != 1 False Yes, I could try to set the Decimal context to 100,000 decimal places -- and just as easily defeat it again by adding one more to the exponent. In my opinion, the Fraction module is one of the least appreciated and underused modules in the standard library -- and I include myself in that. It really is a joy, and I don't use it anywhere near enough. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Raw Unicode docstring
On Nov 16, 1:56 pm, Boštjan Mejak bostjan.me...@gmail.com wrote: Hello, how does one write a raw unicode docstring? If I have backslashes in the docstring, I must tuck an 'r' in front of it, like this: rThis is a raw docstring. If I have foreign letters in the docstring, I must tuck a 'u' in front of it, like this: uThis is a Unicode docstring. What if I have foreign characters *and* backslashes in my docstring? How to write the docstring then? ruMy raw unicode docstring. or urMy unicode docstring. Please answer my question, although it may sound like a noobish one. Thanks. Check out http://cse.csusb.edu/dick/samples/python.syntax.html#stringprefix which lists alternate string prefixes. Does any bodyy know if ur and UR mean the same thing? -- http://mail.python.org/mailman/listinfo/python-list
Re: Help Documenting Python Syntax
On Nov 9, 8:14 am, Grant Edwards inva...@invalid.invalid wrote: On 2010-11-09, Terry Reedy tjre...@udel.edu wrote: On 11/9/2010 10:26 AM, RJB wrote: I have been trying to redevelop a syntax page for Python at http://cse.csusb.edu/dick/samples/python.syntax.html Page does not load correctly; had to hit refresh to get entire page. It should specify that this is the syntax for Python 2.5. To me the Python language is 3.2. Nope. I just checked, and it's 2.6.5: $ python Python 2.6.5 (release26-maint, Aug 9 2010, 11:06:44) ;) My question is why bother with 2.5? I would think the logical choices would be 3.2 or 2.7 (or maybe 2.6). I'm working from some grammars I've found on the web plus experiments. RJB -- http://mail.python.org/mailman/listinfo/python-list
Help Documenting Python Syntax
I have been trying to redevelop a syntax page for Python at http://cse.csusb.edu/dick/samples/python.syntax.html I would appreciate and encouragement or corrections -- because I know there is at least one gross error in there. By the way, this is part of a suite of language definitions... going back to the 1960's RJBotting Who was PAR in the early 1980's -- http://mail.python.org/mailman/listinfo/python-list
