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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 has_node(self, n, t=None):
 """Return True if the graph, at time t, contains the node n. Parameters n : node t : snapshot id (default None) If None return the presence of the node in the flattened graph. Examples -------- True It is more readable and simpler to use True """

        if t is None:
            try:
                return n in self._node
            except TypeError:
                return False
        else:
            deg = list(self.degree([n], t).values())
            if len(deg) > 0:
                return deg[0] > 0
            else:
                return False