Write a program to calculate the value of an expression step by step in Python:

Question

Enter the string “(2 + 3 * 4) / 2 – (3^2 - 3)”. Export:
                     = (2 + 12) / 2 – (3^2 – 3)
                     = 14/2 – (3^2 – 3)
                      = 7 – (3^2 – 3)
                      = 7 – (9 – 3)
                      = 7 – 6
                      = 1

How should I deal with such results?

Asked By: Bảo Huy

||

Source

Answer 1

Here’s some code that does something slightly like what you asked for:

import ast
import copy

expr = "(2 + 3 * 4) / 2 - (3**2 - 3)"
tree = ast.parse(expr,mode="eval")

class EvalLeaves(ast.NodeTransformer):
    def visit_BinOp(self, node):
        match node:
            case ast.BinOp(left=ast.Constant(), right=ast.Constant()):
                return ast.Constant(eval(compile(ast.Expression(ast.fix_missing_locations(node)), "<input>", "eval")))
            case _:
                return ast.BinOp(left=self.visit(node.left),op=node.op,right=self.visit(node.right))

print(expr)
while True:
    new_tree = EvalLeaves().visit(copy.deepcopy(tree))
    if ast.dump(tree) == ast.dump(new_tree):
        break
    tree = new_tree
    print("=", ast.unparse(new_tree))

Output:

(2 + 3 * 4) / 2 - (3**2 - 3)
= (2 + 12) / 2 - (9 - 3)
= 14 / 2 - 6
= 7.0 - 6
= 1.0

Exercises/problems for the reader:

evaluation order the same as in your example
uses Python syntax, e.g. ** for exponentiation rather than ^

Answered By: Oli

Write a program to calculate the value of an expression step by step in Python:

Question:

Answers: