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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_current_usage_str(self):
 """ Get the a string describing the current usage for this limit. If no usage has been added for this limit, the result will be "<unknown>". If the limit has only one current usage instance, this will be that instance's :py:meth:`~.AwsLimitUsage.__str__` value. If the limit has more than one current usage instance, this will be the a string of the form ``max: X (Y)`` where ``X`` is the :py:meth:`~.AwsLimitUsage.__str__` value of the instance with the maximum value, and ``Y`` is a comma-separated list of the :py:meth:`~.AwsLimitUsage.__str__` values of all usage instances in ascending order. :returns: representation of current usage :rtype: str """

        if len(self._current_usage) == 0:
            return '<unknown>'
        if len(self._current_usage) == 1:
            return str(self._current_usage[0])
        lim_str = ', '.join([str(x) for x in sorted(self._current_usage)])
        s = 'max: {m} ({l})'.format(
            m=str(max(self._current_usage)),
            l=lim_str
        )
        return s