Reverse string-formatting (maybe?)

Dustan DustanGroups at gmail.com
Sun Oct 15 21:17:58 CEST 2006


> Only you know what anomalies will be found in your data-sets.  If
> you know/assert that
>
> -the only stuff in the formatting string is one set of characters
>
> -that stuff in the replacement-values can never include any of
> your format-string characters
>
> -that you're not using funky characters/formatting in your format
> string (such as "%%" possibly followed by an "s" to get the
> resulting text of "%s" after formatting, or trying to use other
> formatters such as the aforementioned "%f" or possibly "%i")
>
> then you should be safe.  It could also be possible (with my
> original replacement of "(.*)") if your values will never include
> any substring of your format string.  If you can't guarantee
> these conditions, you're trying to make a cow out of hamburger.
> Or a pig out of sausage.  Or a whatever out of a hotdog. :)
>
> Conventional wisdom would tell you to create a test-suite of
> format-strings and sample values (preferably worst-case funkiness
> in your expected format-strings/values), and then have a test
> function that will assert that the unformatting of every
> formatted string in the set returns the same set of values that
> went in.  Something like
>
> tests = {
> 	'I was %s but now I am %s' : [
> 		('hot', 'cold'),
> 		('young', 'old'),
> 		],
> 	'He has 3 %s and 2 %s' : [
> 		('brothers', 'sisters'),
> 		('cats', 'dogs')
> 		]
> 	}
>
> for format_string, values in tests:
> 	unformatter = format.replace('%s', '(.*)')
> 	for value_tuple in values:
> 		formatted = format_string % value_tuple
> 		unformatted = unformatter.search(formatted).groups()
> 		if unformatted <> value_tuple:
> 			print "%s doesn't match %s when unformatting %s" % (
> 				unformatted,
> 				value_tuple
> 				format_string)
> 
> -tkc

Thanks for all your help. I've gotten the idea.




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