class Expression:
	expression = ""
	variables = []
	
	def __init__(self, expression_string, variables):
		self.expression = expression_string
		self.variables = variables
		
class Variable:
	VARIABLE_TYPES = {
		"i" : "Interest",
		"I" : "Interest",
		"n" : "Time",
		"N" : "Time"
	}
	
	def __init__(self, name, type, starting_point = 0, ending_point = 0):
		self.name = name
		self.type = type
		self.starting_point = starting_point
		self.ending_point = ending_point
		
	@staticmethod
	def get_variable_type(variable_name):
		if not variable_name in Variable.VARIABLE_TYPES:
			return "Unknown"
		return Variable.VARIABLE_TYPES[variable_name]