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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_padding_lengths(self) -> Dict[str, Dict[str, int]]: """ Returns a dictionary of padding lengths, keyed by field name. Each ``Field`` returns a mapping from padding keys to actual lengths, and we just key that dictionary by field name. """

        lengths = {}
        for field_name, field in self.fields.items():
            lengths[field_name] = field.get_padding_lengths()
        return lengths