split string into multi-character "letters"

MRAB python at mrabarnett.plus.com
Wed Aug 25 22:10:11 CEST 2010


On 25/08/2010 20:46, Jed wrote:
> Hi, I'm seeking help with a fairly simple string processing task.
> I've simplified what I'm actually doing into a hypothetical
> equivalent.
> Suppose I want to take a word in Spanish, and divide it into
> individual letters.  The problem is that there are a few 2-character
> combinations that are considered single letters in Spanish - for
> example 'ch', 'll', 'rr'.
> Suppose I have:
>
> alphabet = ['a','b','c','ch','d','u','r','rr','o'] #this would include
> the whole alphabet but I shortened it here
> theword = 'churro'
>
> I would like to split the string 'churro' into a list containing:
>
> 'ch','u','rr','o'
>
> So at each letter I want to look ahead and see if it can be combined
> with the next letter to make a single 'letter' of the Spanish
> alphabet.  I think this could be done with a regular expression
> passing the list called "alphabet" to re.match() for example, but I'm
> not sure how to use the contents of a whole list as a search string in
> a regular expression, or if it's even possible.  My real application
> is a bit more complex than the Spanish alphabet so I'm looking for a
> fairly general solution.

You can build a regex with:

 >>> '|'.join(alphabet)
'a|b|c|ch|d|u|r|rr|o'

You want to try to match, say, 'ch' before 'c', so you want the longest
first:

 >>> '|'.join(sorted(alphabet, key=len, reverse=True))
'ch|rr|a|b|c|d|u|r|o'

If you were going to match the Spanish alphabet then I would recommend
that you do it in Unicode. Well, any text that's not pure ASCII should
be done in Unicode!



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