coords extract

'convert string of bracketed coordinate pairs to list of coordinate tuple integer pairs'
'format (x1, y1) (x2, y2) ... (xn, yn)'

def next_coords(slice):
    'extract next coordinate pair and return that and remaining text'
    slice = slice.strip()  # just in case
    if not slice.startswith('('):
        raise ValueError("Expecting '(' token next")
    pos_close = slice.find(')')  # find position of next )
    if pos_close == -1:  # a -1 indicates a ) was not found
        raise ValueError("Expecting ')' token next")
    x, _ , y = slice[1:pos_close].partition(',')
    if not x or not y:
        raise ValueError("Expecting coordinates between '()'")
    try:
        coords = int(x), int(y)
    except ValueError:
        raise ValueError("Non-integer(s) found between '()'")
    return coords, slice[pos_close+1:]


def parse_buffer(buffer):
    'build & return list of coord integer pair tuples'
    stack = []
    err_message = ''
    while buffer:
        try:
            coords, buffer = next_coords(buffer)
        except ValueError as e:
            err_message = e
            break
        else:
            stack.append(coords)
    return stack, err_message, buffer


tests = ['  (123, 456)    (67,12) (54,67)   ',
         '()', '(test)', '(test, test)',
         '(23,4),(45,67)', '(23,34)(34.5, 67)']
for test in tests:
    stack, err_message, buffer = parse_buffer(test)
    print(f'\ntest: {test}\nstack: {stack}')
    if err_message:
        print(f'Remaining buffer: {buffer}\n{err_message}')