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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 get_arctic_lib(connection_string, **kwargs):
 """ Returns a mongo library for the given connection string Parameters --------- connection_string: `str` Format must be one of the following: library@trading for known mongo servers library@hostname:port Returns: -------- Arctic library """

    m = CONNECTION_STR.match(connection_string)
    if not m:
        raise ValueError("connection string incorrectly formed: %s" % connection_string)
    library, host = m.group(1), m.group(2)
    return _get_arctic(host, **kwargs)[library]