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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 node_contained_in_layer_area_validation(self):
 """ if layer defines an area, ensure node coordinates are contained in the area """

    # if area is a polygon ensure it contains the node
    if self.layer and isinstance(self.layer.area, Polygon) and not self.layer.area.contains(self.geometry):
        raise ValidationError(_('Node must be inside layer area'))