Soundex algorithm in Python (homework help request)

Question

The US census bureau uses a special encoding called “soundex” to locate information about a person. The soundex is an encoding of surnames (last names) based on the way a su

Answer 1

This is hardly perfect (for instance, it produces the wrong result if the input doesn't start with a letter), and it doesn't implement the rules as independently-testable functions, so it's not really going to serve as an answer to the homework question. But this is how I'd implement it:

>>> def soundex_prepare(s):
        """Prepare string for Soundex encoding.

        Remove non-alpha characters (and the not-of-interest W/H/Y), 
        convert to upper case, and remove all runs of repeated letters."""
        p = re.compile("[^a-gi-vxz]", re.IGNORECASE)
        s = re.sub(p, "", s).upper()
        for c in set(s):
            s = re.sub(c + "{2,}", c, s)
        return s

>>> def soundex_encode(s):
        """Encode a name string using the Soundex algorithm."""
        result = s[0].upper()
        s = soundex_prepare(s[1:])
        letters = 'ABCDEFGIJKLMNOPQRSTUVXZ'
        codes   = '.123.12.22455.12623.122'
        d = dict(zip(letters, codes))
        prev_code=""
        for c in s:
            code = d[c]
            if code != "." and code != prev_code:
                result += code
         if len(result) >= 4: break
            prev_code = code
        return (result + "0000")[:4]