On Wed, 1 Jul 2009 22:02:48 +0200 (CEST), Wojciech Puchar <woj...@wojtek.tensor.gdynia.pl> wrote: >> Using an interactive language like Python you can actually *test* the >> code as you are writing it. This is a major win most of the time. > > could you explain what you mean? You can and you have to test a code on > any language be it bash, ksh python or C
Yes. I mean that one can directly interact with the interpret in a REPL prompt, doing stuff like: >>> import re >>> devre = re.compile(r'(/dev/\S+)\s+(\S+)\s.*$') >>> devre <_sre.SRE_Pattern object at 0x28462780> >>> devre.match('/dev/ad0s1d 1012974 390512 541426 42% /var') <_sre.SRE_Match object at 0x28432e78> >>> devre.match('/dev/ad0s1d 1012974 390512 541426 42% /var').groups() ('/dev/ad0s1d', '1012974') >>> devre = >>> re.compile(r'(/dev/\S+)\s+(\S+)\s+(\S+)\s+(\S+)\s+(\S+)\s+(\S+).*$') >>> devre.match('/dev/ad0s1d 1012974 390512 541426 42% /var').groups() ('/dev/ad0s1d', '1012974', '390512', '541426', '42%', '/var') See how I am 'refining' the initial regular expression without ever leaving the Python prompt? That sort of interactivity is entirely lost when you have to edit a file, save it, switch screen(1) windows or type ^Z to background the editor, run a script, watch it fail and repeat. Then I can keep testing bits and pieces of code: >>> from subprocess import Popen, PIPE >>> pipe = Popen(['df', '-k'], shell=False, stdout=PIPE).stdout >>> for l in pipe: ... m = devre.match(l) ... if m: ... print "device %s, size %ld KB" % (m.group(1), long(m.group(2))) ... device /dev/ad0s1a, size 1012974 KB device /dev/ad0s1d, size 1012974 KB device /dev/ad0s1e, size 2026030 KB device /dev/ad0s1f, size 10154158 KB device /dev/ad0s1g, size 284455590 KB device /dev/md0, size 19566 KB >>> So piping df output to a Python bit of code works! That's nice. Then once I have a 'rough idea' of how I want the script to work, I can refactor a bit the repetitive bits: >>> def devsize(line): ... m = devre.match(line) ... if m: ... return (m.group(1), m.group(2)) ... >>> devsize('/dev/ad0s1d 1012974 390512 541426 42% /var') ('/dev/ad0s1d', '1012974') So here's a short function to return a nice 2-item tuple with two values (device name, number of 1 KB blocks). Can we pipe df output through it? >>> pipe = Popen(['df', '-k'], shell=False, stdout=PIPE).stdout >>> pipe = Popen(['df', '-k'], shell=False, stdout=PIPE).stdout >>> map(devsize, pipe.readlines()) [ None, ('/dev/ad0s1a', '1012974'), None, ('/dev/ad0s1d', '1012974'), ('/dev/ad0s1e', '2026030'), ('/dev/ad0s1f', '10154158'), ('/dev/ad0s1g', '284455590'), None, None, None, None, None, None, None, None, None, None, None, None, None, None, ('/dev/md0', '19566'), None] >>> It looks we can do that too, but the tuple list may be more useful if we trim the null items in the process: >>> pipe = Popen(['df', '-k'], shell=False, stdout=PIPE).stdout >>> [t for t in map(devsize, pipe.readlines()) if t] [ ('/dev/ad0s1a', '1012974'), ('/dev/ad0s1d', '1012974'), ('/dev/ad0s1e', '2026030'), ('/dev/ad0s1f', '10154158'), ('/dev/ad0s1g', '284455590'), ('/dev/md0', '19566') ] So there it is. A nice structure, supported by the core of the language, using a readable, easy syntax, and listing all the /dev nodes of my laptop along with their sizes in KBytes. The entire thing was built 'piece by piece', in the same Python session, and I now have not only a 'rough idea' of how the code should work, but also a working copy of the code in my history. Note the complete *lack* of care about how to append to a list, how to create dynamic pairs of devicename-size tuples, how to map all elements of a list through a function, and more importantly the complete and utter lack of any sort of '"${[]}"' quoting for variable names, values, nested expansions, and so on. That's what I am talking about. Shell scripts are nice, but if we are not constrained for some reason to use only /bin/sh or ksh, there's no excuse for wasting hours upon hours to decipher cryptic quoting rules and exceptional edge-cases of "black quoting magic", just to get a short job done. Being able to _easily_ use higher level structures than a plain 'stream of bytes' is nice :) _______________________________________________ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"