Handling errors

Lesson 24 of 29 in Coddy's Calculator project using Python course.

Last step - handling the errors.

In this function most of the errors handled by other function, the only error we should raise is on not matching open and closed parenthesis.

Examples:

parse('3+(1*2')
parse('3+5)')
parse('2*(3+(2-1))+1)')

Adding to parse function this handling can be very hard, so let's create another function which will be called before.

Challenge

Easy

Create a function pre_parse which gets a string and raise an error in case the parenthesis not matching, the function should not return anything.

Raise the exception with the message 'Not matching parenthesis'.

Try it yourself

def calc(op, n1, n2=None):
    if not isinstance(n1, int) and not isinstance(n1, float):
        raise Exception('Invalid number "' + str(n1) + '"')

    if n2 is None:
        if op == '+' or op == 'add':
            return n1
        if op == '-' or op == 'sub':
            return -n1

        raise Exception('Invalid operator "' + op + '"')

    if not isinstance(n2, int) and not isinstance(n2, float):
        raise Exception('Invalid number "' + str(n2) + '"')

    if op == '+' or op == 'add':
        return n1 + n2
    if op == '-' or op == 'sub':
        return n1 - n2
    if op == '*' or op == 'mul':
        return n1 * n2
    if op == '/' or op == 'div':
        if n2 == 0:
            raise Exception("Division by zero")
        return n1 / n2
    if op == '%' or op == 'mod':
        if n2 == 0:
            raise Exception("Division by zero")
        return n1 % n2
    if op == '^' or op == 'pow':
        return n1 ** n2

    raise Exception('Invalid operator "' + op + '"')


def eval(lst):
    if not isinstance(lst, list):
        raise Exception('Failed to evaluate "' + str(lst) + '"')
    if len(lst) == 2:
        op = lst[0]
        n = lst[1]
        if not isinstance(n, list):
            return calc(op, n)

        if isinstance(n, list):
            n = eval(n)

        return calc(op, n)
    elif len(lst) == 3:
        op = lst[0]
        n1 = lst[1]
        n2 = lst[2]
        if not isinstance(n1, list) and not isinstance(n2, list):
            return calc(op, n1, n2)
        
        if isinstance(n1, list):
            n1 = eval(n1)
        if isinstance(n2, list):
            n2 = eval(n2)

        return calc(op, n1, n2)
    else:
        raise Exception('Failed to evaluate "' + str(lst) + '"')


LEVEL_TWO_OPERATORS = ['+', '-', 'add', 'sub']
LEVEL_ONE_OPERATORS = ['*', '/', '%', 'mul', 'div', 'mod']
FUNCTIONS_OPERATORS = ['^', 'pow']
def struct(lst):
    if not isinstance(lst, list) or len(lst) <= 1:
        raise Exception('Failed to structure "' + str(lst) + '"')

    if len(lst) == 2:
        return lst

    lst_cpy = lst
    operators_groups = [FUNCTIONS_OPERATORS, LEVEL_ONE_OPERATORS, LEVEL_TWO_OPERATORS]
    for operators_group in operators_groups:
        i = 0
        while i < len(lst):
            if lst[i] in operators_group:
                if len(lst) - 1 == i:
                    raise Exception('Failed to structure "' + str(lst_cpy) + '"')
                if len(lst) == 3:
                    return [lst[i], lst[i - 1], lst[i + 1]]
                temp = lst[:i - 1]
                temp.append([lst[i], lst[i - 1], lst[i + 1]])
                temp += lst[i + 2:]
                lst = temp
            else:
                i += 1

    return lst


NUMBERS = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
PARENTHESIS = ['(', ')']
def get_next(s, i):
    if i >= len(s):
        raise Exception('End of string')
    res = ''
    if s[i] in NUMBERS or s[i] == '.':
        is_float = False
        while i < len(s) and (s[i] in NUMBERS or s[i] == '.'):
            res += s[i]
            if s[i] == '.':
                is_float = True
            i += 1

        if is_float:
            return float(res)
        return int(res)
    else:
        while i < len(s) and not (s[i] in NUMBERS or s[i] == '.' or s[i] in PARENTHESIS):
            res += s[i]
            i += 1

        return res


def parse(s):
    s = s.replace(' ', '')
    i = 0
    res = []
    while i < len(s):
        if s[i] in PARENTHESIS:
            if s[i] == ')':
                return struct(res), i
            elif s[i] == '(':
                temp = parse(s[i + 1:])
                i += temp[1] + 2
                res.append(temp[0])
        else:
            temp = get_next(s, i)
            res.append(temp)
            i += len(str(temp))
    return struct(res)