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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_defaults(self, x_only=True):
 		""" 		Checks if charts defaults are set 		"""

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