<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def read(self, nodes=None, **kwargs):
 """Load datasets from the necessary reader. Args: nodes (iterable):
 DependencyTree Node objects **kwargs: Keyword arguments to pass to the reader's `load` method. Returns: DatasetDict of loaded datasets """

        if nodes is None:
            required_nodes = self.wishlist - set(self.datasets.keys())
            nodes = self.dep_tree.leaves(nodes=required_nodes)
        return self._read_datasets(nodes, **kwargs)