Added get_values_from_expr method

calculator.py

def get_values_from_expr(expression):
    if "+" in expression:
        raw_values = expression.split("+")
        print(raw_values)
        # raw_values is a list of operands like ['120 ',' 20'] with extra spaces
        values = list(map(str.strip, raw_values))
    else:
        raw_values = expression.split("-")
        print(raw_values)
        # raw_values is a list of operands like ['120 ',' 20'] with extra spaces
        values = list(map(str.strip, raw_values))
    return values


def calc(expression):
    if '+' in expression:
        value1 = expression.split('+')[0]
        value2 = expression.split('+')[1]
        result = int(value1) + int(value2)
    else:
        value1 = expression.split('-')[0]
        value2 = expression.split('-')[1]
        result = int(value1) - int(value2)
    return result