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interpreter.py
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interpreter.py
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class AbstractExpression:
@staticmethod
def interpret():
pass
# Terminal expression
class Number(AbstractExpression):
def __init__(self, value):
self.value = float(value)
def interpret(self):
return self.value
# Non-terminal expression
class AlgebraExpression(AbstractExpression):
def __init__(self, left, right):
self.left = left
self.right = right
class Add(AlgebraExpression):
def interpret(self):
return self.left.interpret() + self.right.interpret()
class Subtract(AlgebraExpression):
def interpret(self):
return self.left.interpret() - self.right.interpret()
class Multiply(AlgebraExpression):
def interpret(self):
return self.left.interpret() * self.right.interpret()
class Divide(AlgebraExpression):
def interpret(self):
return self.left.interpret() / self.right.interpret()
if __name__ == '__main__':
target = "3 + 5 - 2 * 7 / 5 + 11"
tokens = target.split(" ")
expressions = []
for i in range(len(tokens)):
if i == 0:
expressions.append(Number(tokens[i]))
elif tokens[i] == "+":
expressions.append(Add(expressions.pop(), Number(tokens[i+1])))
elif tokens[i] == "-":
expressions.append(Subtract(expressions.pop(), Number(tokens[i + 1])))
elif tokens[i] == "*":
expressions.append(Multiply(expressions.pop(), Number(tokens[i + 1])))
elif tokens[i] == "/":
expressions.append(Divide(expressions.pop(), Number(tokens[i + 1])))
result = expressions.pop().interpret()
print(result)