On Fri, 28 Aug 2009, qwe rty wrote: > i know that an interpreted language like python can't be used to make > an operating system or system drivers. > > what else can NOT be done in python? what are the limitations of the > language?
Oh, my. And now everybody points at you this Turing-completeness. The issue, in my opinion, is not that something cannot be done. The truth about Turing-completeness is, I would say, you can do whatever but sometimes you will not because it would be too ugly. My private list of things that when implemented in Python would be ugly to the point of calling it difficult: 1. AMB operator - my very favourite. In one sentence, either language allows one to do it easily or one would not want to do it (in an ugly way). http://www.randomhacks.net/articles/2005/10/11/amb-operator After quite some googling I was finally able to locate sample implementation, but I cannot say ATM how well it works and if it is practical enough to use it in any of my programs. If time permits, I will try it, hopefully. http://www.c2.com/cgi/wiki?AmbInPython 2. Changing the language from the inside. Everybody can change the interpreter, right? But how about doing some bigger, maybe even fundamental change to the language by means offered by the language itself? Example: If Python had no object system, or if I wanted to implement one in different way (say, I would like to experiment or I would not want to wait for a new release). In some languages that interest me now, it is possible and practical, more or less. So it can sometimes backfire - what OO system should I choose for my next Scheme program, etc. Because there are few of them :-), all (? - I believe) implemented as a code library. Just install it and off you go, now you have OO programming. Actually, I don't use OO all that much recently (maybe I feel disapointed a bit, or something). Also, I have read (but not checked it myself) that for some time Common Lisp had it's now-official CLOS distributed and tested in a form of library. Say, have they adopted OO with single inheritance as a part of CL ANSI standard - I would still be able to have OO with multiple inheritance. I would just have to download and install CLOS. No change to interpreter or compiler. From their point of view, CLOS would be just another library. http://en.wikipedia.org/wiki/Common_Lisp_Object_System Judging by this code, introducing OO to the language is relatively easy: http://www.ccs.neu.edu/home/dorai/t-y-scheme/t-y-scheme-Z-H-14.html It is not possible to alter Python in a minor way, I think. Something simpler than OO, like a new keyword or structures: http://www.ccs.neu.edu/home/dorai/t-y-scheme/t-y-scheme-Z-H-10.html http://www.ccs.neu.edu/home/dorai/t-y-scheme/t-y-scheme-Z-H-11.html Some readers could oppose the above by saying that Lisp's syntax is so primitive that it can be used to implement just any programming paradigm, so having it as a loadable code is not a big achievement. Well, it seems to me that Python has even simpler syntax or on par with Lisp family, so... Some (perhaps other) readers could also say, that there is no need to extend Python. It already has sets and "yield" and... But some time ago it did not. As far as I can tell, it can be a bit too hard to go into "experimenting mode" with Python. Something like adding "yield" all but myself. It only takes few kilos of code for a working OO in another language, so how hard could such "yield" be? Well, in Python I probably wouldn't dare. BTW I hope nobody's feeling have been hurt. This was meant to be informative, not offensive. BTW2. As I said, these are _possible_ things (Turing complete language, and so on). But adding them would require some hard work and would produce ugly and/or fragile code, so I decided it could be easier to learn another language... Regards, Tomasz Rola -- ** A C programmer asked whether computer had Buddha's nature. ** ** As the answer, master did "rm -rif" on the programmer's home ** ** directory. And then the C programmer became enlightened... ** ** ** ** Tomasz Rola mailto:tomasz_r...@bigfoot.com ** -- http://mail.python.org/mailman/listinfo/python-list
