Calc str examples

def define(example):
    if '--' in example:
        result_arr = example.split('--')
        result = ''
        for ex in result_arr:
            result += ex + '+'
        return define(result[: len(result) - 1])
    try:
        result = int(example)
        return result
    except ValueError:
        if '(' not in example:
            if '*' in example:
                index = example.find('*')
                for j in range(index - 1, -1, -1):
                    try:
                        check = int(example[j])
                        if j is 0:
                            first_number = int(example[j : index])
                            start_first_number = j
                    except ValueError:
                        if example[j] is '-':
                            first_number = int(example[j : index])
                            start_first_number = j
                            break
                        else:
                            first_number = int(example[j + 1 : index])
                            start_first_number = j + 1
                            break
                if example[index + 1] is '-':
                    for j in range(index + 2, len(example)):
                        try:
                            check = int(example[j])
                            if j is len(example) - 1:
                                second_number = int(example[index + 1 :])
                                finish_second_number = j
                        except ValueError:
                            second_number = int(example[index + 1 : j])
                            finish_second_number = j - 1
                            break
                else:
                    for j in range(index + 1, len(example)):
                        try:
                            check = int(example[j])
                            if j is len(example) - 1:
                                second_number = int(example[index + 1 :])
                                finish_second_number = j
                        except ValueError:
                            second_number = int(example[index + 1 : j])
                            finish_second_number = j - 1
                            break
                result_number = first_number * second_number
                example = example[:start_first_number] + str(result_number) + example[finish_second_number + 1 :]
                return define(example)



            elif '+' in example:
                index = example.find('+')
                for j in range(index - 1, -1, -1):
                    try:
                        check = int(example[j])
                        if j is 0:
                            first_number = int(example[j : index])
                            start_first_number = j
                    except ValueError:
                        if example[j] is '-':
                            first_number = int(example[j : index])
                            start_first_number = j
                            break
                        else:
                            first_number = int(example[j + 1 : index])
                            start_first_number = j + 1
                            break
                if example[index + 1] is '-':
                    for j in range(index + 2, len(example)):
                        try:
                            check = int(example[j])
                            if j is len(example) - 1:
                                second_number = int(example[index + 1 :])
                                finish_second_number = j
                        except ValueError:
                            second_number = int(example[index + 1 : j])
                            finish_second_number = j - 1
                            break
                else:
                    for j in range(index + 1, len(example)):
                        try:
                            check = int(example[j])
                            if j is len(example) - 1:
                                second_number = int(example[index + 1 :])
                                finish_second_number = j
                        except ValueError:
                            second_number = int(example[index + 1 : j])
                            finish_second_number = j - 1
                            break
                result_number = first_number + second_number
                example = example[:start_first_number] + str(result_number) + example[finish_second_number + 1 :]
                return define(example)



            else:
                index = example.rfind('-')
                for j in range(index - 1, -1, -1):
                    try:
                        check = int(example[j])
                        if j is 0:
                            first_number = int(example[j : index])
                            start_first_number = j
                    except ValueError:
                        if example[j] is '-':
                            first_number = int(example[j : index])
                            start_first_number = j
                            break
                        else:
                            first_number = int(example[j + 1 : index])
                            start_first_number = j + 1
                            break
                if example[index + 1] is '-':
                    for j in range(index + 2, len(example)):
                        try:
                            check = int(example[j])
                            if j is len(example) - 1:
                                second_number = int(example[index + 1 :])
                                finish_second_number = j
                        except ValueError:
                            second_number = int(example[index + 1 : j])
                            finish_second_number = j - 1
                            break
                else:
                    for j in range(index + 1, len(example)):
                        try:
                            check = int(example[j])
                            if j is len(example) - 1:
                                second_number = int(example[index + 1 :])
                                finish_second_number = j
                        except ValueError:
                            second_number = int(example[index + 1 : j])
                            finish_second_number = j - 1
                            break
                result_number = first_number - second_number
                example = example[:start_first_number] + str(result_number) + example[finish_second_number + 1 :]
                return define(example)
        else:
            index1 = example.rfind('(')
            index2 = example.find(')', example.rfind('('), len(example))
            result_number = define(example[index1 + 1 : index2])
            example = example[:index1] + str(result_number) + example[index2 + 1 :]
            return define(example)