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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 uri_from_fields(prefix, *fields):
 """Construct a URI out of the fields, concatenating them after removing offensive characters. When all the fields are empty, return empty"""

        string = '_'.join(AlignmentHelper.alpha_numeric(f.strip().lower(), '') for f in fields)

        if len(string) == len(fields) - 1:
            return ''

        return prefix + string