Adding two numbers using a randomised operator

Question

The following is my code, and it works. It creates two random numbers, a random operator and puts them together, however it does not sum them after doing this. What I need is for the program to recognise it as an equation, rather than simply printing out the individual variables.

So, to avoid confusion; my question is: How would I get firstNumber and secondNumberto be summed together using whatever operator is selected, rather than simply printing them out together?

from random import choice
from random import randint

ranOperator = ["*", "/", "+", "-"]

def askQuestion():
    firstNumber = randint(1,10)
    secondNumber = randint(1,10)
    operator = choice(ranOperator)

    generateQuestion = ' '.join((str(firstNumber), operator, str(secondNumber)))
    print(generateQuestion)

askQuestion()

Current output (example):

4 + 3

Using the same numbers above, what I would want to happen:

Can you update the question to give an example of both the current output and the desired output? — quamrana, Feb 21 '18 at 11:54
Possible duplicate of [Evaluating a mathematical expression in a string](https://stackoverflow.com/questions/2371436/evaluating-a-mathematical-expression-in-a-string) — Georgy, Feb 21 '18 at 13:18

score 7 · Answer 1 · answered Feb 21 '18 at 11:58

7

One way to not rely on eval is using the operator module to represent the operations.

from random import choice
from random import randint
from operator import add, sub, truediv, mul

ranOperator = [add, sub, truediv, mul]

def askQuestion():
    firstNumber = randint(1,10)
    secondNumber = randint(1,10)
    the_operator = choice(ranOperator)

    result = the_operator(firstNumber, secondNumber)
    print(result)

answered Feb 21 '18 at 11:58

dseuss

971
6
8

plus 1 since it more safe – Matt. Stroh Feb 21 '18 at 12:13

Austin · Answer 2 · 2018-02-21T12:01:51.820

3

What you need is eval().

eval() evaluates the passed string as a Python expression and returns the result.

from random import choice
from random import randint

ranOperator = ["*", "/", "+", "-"]

def askQuestion():
    firstNumber = randint(1,10)
    secondNumber = randint(1,10)
    operator = choice(ranOperator)

    generateQuestion = ' '.join((str(firstNumber), operator, str(secondNumber)))
    print(eval(generateQuestion))

askQuestion()

Demo:

>>> eval('1+1')
2
>>> eval('5-3')
2
>>> eval('2*3')
6
>>> eval('6/3')
2

edited Feb 21 '18 at 12:01

answered Feb 21 '18 at 11:56

Austin

25,759
4
25
48

Just adding that eval can be dangerous - https://nedbatchelder.com/blog/201206/eval_really_is_dangerous.html – Matt. Stroh Feb 21 '18 at 12:12
Fortunately in this case all the inputs to `eval` are controlled by the program. (Still, not an excuse to use eval when the `operator` module is available) – quamrana Feb 21 '18 at 12:19
@quamrana @Matt. Stroh In this context, it does not matter if you use `eval` - not dangerous as you say. After all, we want our work to be done. If it can be done (safe here), why bother about danger! – Austin Feb 21 '18 at 12:22
@theausome Unfortunately its not about *this* case, its about the case in the future where the program is 'extended' and includes uncontrolled input. – quamrana Feb 21 '18 at 12:25

Uday Krishna · Answer 3 · 2018-03-11T15:47:53.383

Extending dseuss's answer to incorporate any function and print a math-like equation by mapping a function to its symbol using a dictionary

from random import choice
from random import randint

add = lambda x,y: x+y
substract = lambda x,y: x-y
divide = lambda x,y: x/y
multiply = lambda x,y: x*y

ranOperator = {"*":multiply, "/":divide, "+":add, "-":substract}

def askQuestion():
    firstNumber = randint(1,10)
    secondNumber = randint(1,10)
    operator_key = choice(list(ranOperator.keys()))

    answer = ranOperator[operator_key](firstNumber,secondNumber)
    print("{} {} {} = {}".format(firstNumber, operator_key, secondNumber, answer))

askQuestion()

Adding two numbers using a randomised operator

3 Answers3