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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 addField(self, field) : 		"""add a filed to the legend"""

		if field.lower() in self.legend :
			raise  ValueError("%s is already in the legend" % field.lower())
		self.legend[field.lower()] = len(self.legend)
		if len(self.strLegend) > 0 :
			self.strLegend += self.separator + field
		else :
			self.strLegend += field