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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 set_local(self, key=None, value=None, data=None, **kwdata):
 """ Locally store some data associated with this conversation. Data can be passed in either as a single dict, or as key-word args. For example, if you need to store the previous value of a remote field to determine if it has changed, you can use the following:: prev = conversation.get_local('field') curr = conversation.get_remote('field') if prev != curr: handle_change(prev, curr) conversation.set_local('field', curr) Note: This uses :mod:`charmhelpers.core.unitdata` and requires that :meth:`~charmhelpers.core.unitdata.Storage.flush` be called. :param str key: The name of a field to set. :param value: A value to set. This value must be json serializable. :param dict data: A mapping of keys to values. :param **kwdata: A mapping of keys to values, as keyword arguments. """

        if data is None:
            data = {}
        if key is not None:
            data[key] = value
        data.update(kwdata)
        if not data:
            return
        unitdata.kv().update(data, prefix='%s.%s.' % (self.key, 'local-data'))