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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 grid(self, z_x_y):
 """ Return the UTFGrid content """

        # sources.py -> MapnikRenderer -> grid
        (z, x, y) = z_x_y
        content = self.reader.grid(z, x, y, self.grid_fields, self.grid_layer)
        return content