DO NOT CHANGE FUNCTION NAMES, ARGUMENTS and the things given in the starter code.

Calculator Class (Python):

Implement a class that calculates mathematic expressions. The input passed to this Calculator is in infix notation, which gets converted to postfix internally, then the postfix expression is evaluated.

setExpr(self, new_expr) - Sets the expression for the calculator to evaluate. This method is already implemented for you.

getExpr(self) - Property method for getting the expression in the calculator. This method is already implemented for you.

isNumber(self, txt) - Returns True if txt is a string that can be converted to a float, False otherwise.

_getPostfix(self, expr) - Converts an expression from infix to postfix. All numbers in the output must be represented as a float.

calculate(self) - A property method that evaluates the infix expression saved in self.__expr. First convert the expression to postfix, then use a stack to evaluate the output postfix expression.

STARTER CODE:

Attributes Type Name str expr Description The expression this calculator will evaluate Methods Type Name Description None setExpr(self, new_expr) Sets the expression for the calculator to evaluate getExpr(self) Getter method for the private expression attribute bool isNumber(self, txt) Returns True if txt can be converted to a float _getPostfix(self, expr) Converts an expression from infix to postfix float calculate(self) Calculates the expression stored in this calculator str str class Calculator: def __init_(self): self._expr None @property def getExpr(self): return self._expr def setExpr(self, new_expr): if isinstance(new_expr, str): self._expr=new_expr else: print('setExpr error: Invalid expression') return None def isNumber(self, txt): pass def _getPostfix(self, txt): postOp = Stack() pass @property def calculate(self): if not isinstance(self._expr,str) or len(self._expr)