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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 _check_fields(self, x, y):
 		""" 		Check x and y fields parameters and initialize 		"""

		if x is None:
			if self.x is None:
				self.err(
					self._check_fields,
					"X field is not set: please specify a parameter")
				return
			x = self.x
		if y is None:
			if self.y is None:
				self.err(
					self._check_fields,
					"Y field is not set: please specify a parameter")
				return
			y = self.y
		return x, y