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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 _uncamelize(self, s):
        ''' Convert a camel-cased string to using underscores '''
        res = ''
        if s:
            for i in range(len(s)): 
                if i > 0 and s[i].lower() != s[i]:
                    res += '_'
                res += s[i].lower()
        return res