tools/calculator.py

import ast
import operator as op
from langchain.tools import Tool

operators = {
    ast.Add: op.add,
    ast.Sub: op.sub,
    ast.Mult: op.mul,
    ast.Div: op.truediv,
    ast.Pow: op.pow,
    ast.Mod: op.mod,
    ast.USub: op.neg,
}

def safe_eval(expr: str) -> float:
    """
    Safely evaluate a mathematical expression string.
    Supports +, -, *, /, **, %, and negative numbers.
    """
    def eval_node(node):
        if isinstance(node, ast.Num):  # <number>
            return node.n
        elif isinstance(node, ast.BinOp):  # <left> <operator> <right>
            return operators[type(node.op)](eval_node(node.left), eval_node(node.right))
        elif isinstance(node, ast.UnaryOp):  # <operator> <operand> e.g., -1
            return operators[type(node.op)](eval_node(node.operand))
        else:
            raise TypeError(f"Unsupported type: {node}")

    try:
        node = ast.parse(expr, mode='eval').body
        return eval_node(node)
    except Exception as e:
        return f"[Calculator error: {e}]"

def calculator(query: str) -> str:
    try:
        result = safe_eval(query)
        return str(result)
    except Exception as e:
        return f"[Calculator error: {e}]"

calculator_tool = Tool.from_function(
    name="calculator",
    description="Performs safe mathematical calculations from a text query. Supports +, -, *, /, %, and powers.",
    func=calculator
)