function with operators as parameter

Question

i just started coding for fun and i'm trying to build a calculator that uses userinput. 2 numbers and one operator. I'm realy realy new to coding and currently limited to very simple use of if statements and while/for loops and i just started looking into functions. I have been trying to put this code into a function for a while but i can't find a solution to use the string "operator" as an actual operator in the function.

there must be a way to make all of this shorter.

if used_op == "+":
    print(">  " + str(number_1) + " + " + str(number_2) + " = " + str(number_1 + number_2) + "  <")
elif used_op == "-":
    print(">  " + str(number_1) + " - " + str(number_2) + " = " + str(number_1 - number_2) + "  <")
elif used_op == "*":
    print(">  " + str(number_1) + " * " + str(number_2) + " = " + str(number_1 * number_2) + "  <")
elif used_op == "/":
    print(">  " + str(number_1) + " / " + str(number_2) + " = " + str(number_1 / number_2) + "  <")
elif used_op == "%":
    print(">  " + str(number_1) + " % " + str(number_2) + " = " + str(number_1 % number_2) + "  <")
elif used_op == "**":
    print(">  " + str(number_1) + " ** " + str(number_2) + " = " + str(number_1 ** number_2) + "  <")
elif used_op == "//":
    print(">  " + str(number_1) + " // " + str(number_2) + " = " + str(number_1 // number_2) + "  <")

What I tried is something like this:

def solve(op):
    print(">  " + str(number_1) + op + str(number_2) + " = " + str(
        number_1 + **op** + number_2) + "  <")

solve(used_op)

I tried to find a solution for this on the internet for a while but i had no luck so far.

C.Nivs · Accepted Answer · 2019-02-26 04:06:46Z

2

You can use a dictionary and the operator module to do what you want:

import operator

# this will act like a sort of case statement or switch
operations = {
    '>': operator.gt,
    '<': operator.lt,
    '=': operator.eq,
    '+': operator.add,
    '-': operator.sub,
    '/': operator.div,
    '*': operator.mul,
    '**': operator.pow,
    '//': operator.floordiv,
    ... # so on and so forth
}

def calculate(num1, num2, op):
    # operation is a function that is grabbed from the dictionary
    operation = operations.get(op)
    if not operation:
         raise KeyError("Operation %s not supported"%op)

    # Call the operation with your inputs
    num3 = operation(num1, num2)
    print('%3.2f %s %3.2f = %3.2f' % (num1, op, num2, num3))


calculate(1,2, '+')
# 1.00 + 2.00 = 3.00

edited Feb 26, 2019 at 4:06

answered Feb 26, 2019 at 3:59

C.Nivs

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Comments

Mantas Kandratavičius · Accepted Answer · 2019-02-26 04:05:05Z

-1

Simply evaluate your mathematical expression and python will do the rest of the job for you.

This can of course be done with the in-built eval() function.

Here are some examples how you can use it:

>>> eval("1+1")
2

>>> A = 2
>>> eval("A * 3")
6

The function that you're trying to write, could look something like this

def solve(a, b, op):
    expression = str(a) + op + str(b)
    print("> " + expression + "=" + str(eval(expression)))

solve(1, 2, "+")   # > 1+2=3
solve(10, 10, "*") # > 10*10=100
solve(4, 2, "/")   # > 4/2=2.0
solve(5, 10, "-")  # > 5-10=-5

answered Feb 26, 2019 at 4:05

Mantas Kandratavičius

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6 Comments

Deeze Over a year ago

i like this alot! looks very clean and elegant.

Mantas Kandratavičius Over a year ago

No problem! It's worth noting that the previously accepted answer is generally speaking more "proffesional", however when it comes to simplicity, I would say this is the way to go.

Deeze Over a year ago

to be honest i'm just not there yet, to really understand the other answer. i tryed it out and it worked. but i should understand it in order to use it.

C.Nivs Over a year ago

I'd agree that this answer is quite simple and easy to read. However, eval is usually seen as a bad practice and not something to be used lightly. For this example, there's no harm, just a heads up in future answers

Deeze Over a year ago

well i'm sad now, i wrote a calculator programm with 80 lines and it took me like 5h. and its far from perfect. now i realized that: expression = input("Enter calc: ") print("> " + expression + " = " + str(eval(expression)) + " <") does everything and more then my program :)

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