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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 _verify(self, path_prefix=None):
 """Verifies that this schema's doc spec is valid and makes sense."""

        for field, spec in self.doc_spec.iteritems():
            path = self._append_path(path_prefix, field)

            # Standard dict-based spec
            if isinstance(spec, dict):
                self._verify_field_spec(spec, path)
            else:
                raise SchemaFormatException("Invalid field definition for {}", path)