Calculator in python

Question

I am trying to make calculator that can solve expressions with basic 4 operators, like 1+2*3-4/5, however it does not work and I do not know what is wrong. Please check my code.

Answer 1

The main thing you are doing wrong is that you are checking the value of c rather that the partitioned operator. You can also unpack the result from s.partition to make things a little easier by using left and right for the actual operations.

def ret(s):
    s = str(s)
    if s.isdigit():
        return float(s)
    for c in ('-','+','*','/'):
        left, op, right = s.partition(c)
        if op == '*':
            return ret(left) * ret(right)
        elif op == '/':
            return ret(left) / ret(right)
        elif op == '+':
            return ret(left) + ret(right)
        elif op == '-':
            return ret(left) - ret(right)
print(ret('1+2'))

Also, you will need to reverse the order of your operations as you want to first do addition and subtraction, followed by multiplication and division.

What I mean is, if you have an expression like 4+4*3, you want to divide it into

ret(4) + ret(4 * 3)

Since it is a recursive call, you want the operators with the highest precedence to be the last on the call stack so they are executed first when the function returns.

As an example:

print(ret('1+2*6'))
print(ret('3*8+6/2'))

OUTPUT

13.0
27.0