First class was posted in this question, third class will be posted in a different question, please refer to it, thank you: https://www.bartleby.com/questions-and-answers/computer-science-question/34b2a175-1365-4989-a811-33c7e8b66a7bDo not change the function names or given starter code in the script. Each class has different requirements, read them carefully. Do not use the exec or eval functions, nor are you allowed to use regular expressions (re module). All methods that output a string must return the string, not print it. If you are unable to complete a method, use the pass statement to avoid syntax errors. Section 2: The Calculator class 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 (we evaluate in postfix instead of infix because of how much simpler it is). More details about infix to postfix conversion can be found in the video lectures. This calculator should support numeric values, five arithmetic operators (+, –, *, /, ^), and parenthesis. Follow the PEMDAS order of operations (you can define precedence of operators with a dictionary or a helper method). Note that exponentiation is ** in Python. You can assume that expressions will have tokens (operators, operands) separated by a single space. For the case of negative numbers, you can assume the negative sign will be prefixed to the number. The str.split() method can be helpful to isolate tokens. Expressions are considered invalid if they meet any of the following criteria: • Contains unsupported operators 4 $ 5 • Contains consecutive operators 4 * + 5 • Has missing operands 4 + • Has missing operators 4 5 • Has unbalanced parenthesis ) 4 + 5 ( or ( 4 + 5 ) ) • Tries to do implied multiplication 3(5) instead of 3 * ( 5 ) • Includes a space before a negative number 4 * - 5 instead of 4 * -5 Make sure to have proper encapsulation of your code by using proper variable scopes and writing other helper methods to generalize your code for processes such as string processing and input validation. Do not forget to document your code. As a suggestion, start by implementing your methods assuming the expressions are always valid, that way you have the logic implemented and you only need to work on validating the expressions. Attributes Type Name Description str __expr The expression this calculator will evaluate Methods Type Name Description None setExpr(self, new_expr) Sets the expression for the calculator to evaluate str getExpr(self) Getter method for the private expression attribute bool _isNumber(self, aSring) Returns True if aSring can be converted to a float str _getPostfix(self, expr) Converts an expression from infix to postfix float calculate(self) Calculates the expression stored in this calculator setExpr(self, new_expr) Sets the expression for the calculator to evaluate. This method is already implemented for you. Input (excluding self) str new_expr The new expression (in infix) for the calculator to evaluate getExpr(self) Property method for getting the expression in the calculator. This method is already implemented for you. Output str The value stored in __expr _isNumber(self, txt) Returns True if txt is a string that can be converted to a float, False otherwise. Note that the type conversion float('4.56') returns 4.56 but float('4 56') raises an exception. A try/except block could be useful here. Input (excluding self) str txt The string to check if it represents a number Output bool True if txt can be successfully casted 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. You must use the Stack defined in section 1 in this method, otherwise your code will not receive credit. (Stack applications video lecture can be helpful here). Input (excluding self) str expr The expression in infix form Output str The expression in postfix form None None is returned if the input is an invalid expression 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. You must use the Stack defined in section 1 in this method, otherwise your code will not receive credit. Input (excluding self) str txt The string to check if it represents a number Output float The result of the expression None None is returned if the input is an invalid expression or if expression can’t be computed

Question

First class was posted in this question, third class will be posted in a different question, please refer to it, thank you: https://www.bartleby.com/questions-and-answers/computer-science-question/34b2a175-1365-4989-a811-33c7e8b66a7bDo not change the  function names or given starter code in the script. Each class has different requirements, read them carefully. Do not use the exec or eval functions, nor are you allowed to use regular expressions (re module).  All methods that output a string must return the string, not print it. If you are unable to complete a method, use the pass statement to avoid syntax errors.  Section 2: The Calculator class 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 (we evaluate in postfix instead of infix because of how much simpler it is). More details about infix to postfix conversion can be found in the video lectures. This calculator should support numeric values, five arithmetic operators (+, –, *, /, ^), and parenthesis. Follow the PEMDAS order of operations (you can define precedence of operators with a dictionary or a helper method). Note that exponentiation is ** in Python. You can assume that expressions will have tokens (operators, operands) separated by a single space. For the case of negative numbers, you can assume the negative sign will be prefixed to the number. The str.split() method can be helpful to isolate tokens. Expressions are considered invalid if they meet any of the following criteria: • Contains unsupported operators 4 $ 5 • Contains consecutive operators 4 * + 5 • Has missing operands 4 + • Has missing operators 4 5 • Has unbalanced parenthesis ) 4 + 5 ( or ( 4 + 5 ) ) • Tries to do implied multiplication 3(5) instead of 3 * ( 5 ) • Includes a space before a negative number 4 * - 5 instead of 4 * -5 Make sure to have proper encapsulation of your code by using proper variable scopes and writing other helper methods to generalize your code for processes such as string processing and input validation. Do not forget to document your code. As a suggestion, start by implementing your methods assuming the expressions are always valid, that way you have the logic implemented and you only need to work on validating the expressions. Attributes Type Name Description str __expr The expression this calculator will evaluate Methods Type Name Description None setExpr(self, new_expr) Sets the expression for the calculator to evaluate str getExpr(self) Getter method for the private expression attribute bool _isNumber(self, aSring) Returns True if aSring can be converted to a float str _getPostfix(self, expr) Converts an expression from infix to postfix float calculate(self) Calculates the expression stored in this calculator  setExpr(self, new_expr) Sets the expression for the calculator to evaluate. This method is already implemented for you. Input (excluding self) str new_expr The new expression (in infix) for the calculator to evaluate getExpr(self) Property method for getting the expression in the calculator. This method is already implemented for you. Output str The value stored in __expr _isNumber(self, txt) Returns True if txt is a string that can be converted to a float, False otherwise. Note that the type conversion float('4.56') returns 4.56 but float('4 56') raises an exception. A try/except block could be useful here. Input (excluding self) str txt The string to check if it represents a number Output bool True if txt can be successfully casted 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. You must use the Stack defined in section 1 in this method, otherwise your code will not receive credit. (Stack applications video lecture can be helpful here). Input (excluding self) str expr The expression in infix form Output str The expression in postfix form None None is returned if the input is an invalid expression  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. You must use the Stack defined in section 1 in this method, otherwise your code will not receive credit. Input (excluding self) str txt The string to check if it represents a number Output float The result of the expression None None is returned if the input is an invalid expression or if expression can’t be computed

Accepted Answer

Here is Solution for above program :
class Calculator:
    def _init_(self):
        self._expr=None…