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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 camelcase_to_underscores(word):
 """Converts a CamelCase word into an under_score word. 'camel_case_case' 'get_http_response_code' """

    s1 = _FIRST_CAP_RE.sub(r'\1_\2', word)
    return _ALL_CAP_RE.sub(r'\1_\2', s1).lower()