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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 snake_case(a_string):
 """Returns a snake cased version of a string. :param a_string: any :class:`str` object. Usage: "foo_bar" """


    partial = re.sub('(.)([A-Z][a-z]+)', r'\1_\2', a_string)
    return re.sub('([a-z0-9])([A-Z])', r'\1_\2', partial).lower()