The bones of a nice Python script

Developing a nice template for new scripts

#!/usr/bin/python import sys import random def scramble(word): if len(word) < 4: return word innards = list(word[1:-1]) random.shuffle(innards) return word[0] + ''.join(innards) + word[-1] while 1: line = sys.stdin.readline() if not line: break sys.stdout.write(' '.join([scramble(w) for w in line.split()]) + ' ') In the beginning

Adding basic niceties #!/usr/bin/ env python # -*- coding: utf-8 -*- import sys import random def scramble(word): if len(word) < 4: return word innards = list(word[1:-1]) random.shuffle(innards) return word[0] + ''.join(innards) + word[-1] def _main(): while 1: line = sys.stdin.readline() if not line: break sys.stdout.write(' '.join([scramble(w) for w in line.split()]) + ' ') return 0 if __name__ == "__main__": sys.exit(_main())

stephenj@lords:~$ python Python 2.5.2 (r252:60911, Oct 5 2008, 19:24:49) [GCC 4.3.2] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import scramble >>> scramble.scramble('scramble') 'srlacmbe' >>>

from optparse import OptionParser ... def _main(filename=None): ... if __name__ == "__main__": usage = "usage: %prog [options] [filename]" parser = OptionParser(usage=usage) parser.add_option('--profile', '-P', help = "Print out profiling stats", action = 'store_true') parser.add_option('--test', '-t', help ='Run doctests', action = 'store_true') parser.add_option('--verbose', '-v', help ='print debugging output', action = 'store_true') (options, args) = parser.parse_args() # Assign non-flag arguments here. filename = None if len(args) > 0: filename = args[0]

stephenj@lords:~$ python scramble.py -h Usage: scramble.py [options] [filename] Options: -h, --help show this help message and exit -P, --profile Print out profiling stats -t, --test Run doctests -v, --verbose print debugging output

Tests are good def scramble(word): """ Returns a scrambled version if it is longer than 3 chars. Scrambling preserves the first and last characters. >>> scramble('a') 'a' >>> scramble('an') 'an' >>> scramble('the') 'the' >>> scramble('cart') in ['cart', 'crat'] True """ if len(word) < 4: return word innards = list(word[1:-1]) random.shuffle(innards) return word[0] + ''.join(innards) + word[-1] def _test(verbose=False): import doctest doctest.testmod(verbose=verbose)

stephenj@lords:~$ python scramble.py --test --verbose Trying: scramble('a') Expecting: 'a' ok Trying: scramble('an') Expecting: 'an' ok Trying: scramble('the') Expecting: 'the' ok Trying: scramble('cart') in ['cart', 'crat'] Expecting: True ok 5 items had no tests: __main__ __main__._main __main__._profile_main __main__._test __main__.really_blurt 1 items passed all tests: 4 tests in __main__.scramble 4 tests in 6 items. 4 passed and 0 failed. Test passed. stephenj@lords:~$

Now I'm a real boy Unix filter def _blurt(s, f): pass def _main(filename=None): f = sys.stdin if filename: try: f = file(filename) except Exception, ex: print "Couldn't open file %s: %s" % (filename, ex) return 1 while 1: line = f.readline() if not line: break _blurt("Original line was: %s" % line) sys.stdout.write(' '.join([scramble(w) for w in line.split()]) + ' ') return 0 if __name__ == "__main__": ... if options.verbose: def really_blurt(s, f=()): sys.stderr.write(s % f + ' ') _blurt = really_blurt ... if len(args) > 0: filename = args[0] _blurt("filename is %s", filename) sys.exit(_main(filename))

Dealing with performance anxiety def _profile_main(filename=None): import cProfile, pstats prof = cProfile.Profile() ctx = """_main(filename)""" prof = prof.runctx(ctx, globals(), locals()) stats = pstats.Stats(prof) stats.sort_stats("cumulative") stats.print_stats(10) ... if __name__ == "__main__": ... if options.profile: _profile_main(filename) exit()

Making use of our options stephenj@lords:~$ python scramble.py asdf Couldn't open file asdf: [Errno 2] No such file or directory: 'asdf' stephenj@lords:~$ echo $? 1 stephenj@lords:~$ echo "You should probably be able to understand this" | python scramble.py -v Original line was: You should probably be able to understand this You suhold pbrbolay be able to usedanrntd this stephenj@lords:~$ echo "You should probably be able to understand this" | python scramble.py -P You sluohd pbalbroy be albe to unrdentsad tihs 57 function calls in 0.000 CPU seconds Ordered by: internal time List reduced from 12 to 10 due to restriction <10> ncalls tottime percall cumtime percall filename:lineno(function) 5 0.000 0.000 0.000 0.000 /usr/lib/python2.5/random.py:250(shuffle) 8 0.000 0.000 0.000 0.000 scramble.py:16(scramble) 1 0.000 0.000 0.000 0.000 scramble.py:59(_main) 1 0.000 0.000 0.000 0.000 {method 'write' of 'file' objects} 17 0.000 0.000 0.000 0.000 {method 'random' of '_random.Random' objects} 2 0.000 0.000 0.000 0.000 {method 'readline' of 'file' objects} 13 0.000 0.000 0.000 0.000 {len} 6 0.000 0.000 0.000 0.000 {method 'join' of 'str' objects} 1 0.000 0.000 0.000 0.000 <string>:1(<module>) 1 0.000 0.000 0.000 0.000 {method 'split' of 'str' objects}

#!/usr/bin/env python # -*- coding: utf-8 -*- import sys from optparse import OptionParser def _test(verbose=None): import doctest doctest.testmod(verbose=verbose) def _profile_main( filename=None ): import cProfile, pstats prof = cProfile.Profile() ctx = """_main(filename)""" prof = prof.runctx(ctx, globals(), locals()) stats = pstats.Stats(prof) stats.sort_stats("time") stats.print_stats(10) def _blurt(s, f): pass def _main(filename=None): # YOUR CODE HERE return 0 if __name__ == "__main__": usage = "usage: %prog [options] [filename] " parser = OptionParser(usage=usage) parser.add_option('--profile', '-P', help = "Print out profiling stats", action = 'store_true') parser.add_option('--test', '-t', help ='Run doctests', action = 'store_true') parser.add_option('--verbose', '-v', help ='print debugging output', action = 'store_true') (options, args) = parser.parse_args() if options.verbose: def really_blurt(s, f=()): sys.stderr.write(s % f + ' ') _blurt = really_blurt # Assign non-flag arguments here. filename = args[0] if options.profile: _profile_main( filename ) exit() if options.test: _test(verbose=options.verbose) exit() sys.exit(_main( filename ))

Original inspiration Guido's post and subsequent commentary http://www.artima.com/forums/flat.jsp?forum=106&thread=4829 Google app engine help http://code.google.com/appengine/kb/commontasks.html#profiling The scrambled text meme http://www.snopes.com/language/apocryph/cambridge.asp

The bones of a nice Python script

0 comments

Notes on slide 1

2 Favorites & 1 Group