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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def add_prefix(prefix, s):
    "Add `prefix` to all unprefixed names in `s`"
    # tokenize the XPath expression
    toks = xpath_lexer.scan(s)
    # add default prefix to unprefixed names
    toks2 = [_add_prefix(prefix, tok) for tok in toks]
    # build a string of the patched expression
    ls = [x.value for x in toks2]
    return ''.join(ls)