General purpose tuple parser for Python

gistfile1.py

from decimal import Decimal

def _wrap_converter(fn):
    def _wrapper(elem):
        try:
            return fn(elem)
        except Exception as e:
            msg = "Failed to convert value {0}: {1}".format(
                elem, e)
            raise ValueError(msg)
    return _wrapper

class TupleParser(object):
    def __init__(self, converter=None, size=None, separator=","):
        self._identity = lambda e: e
        self.converter = _wrap_converter(converter or self._identity)
        self.size = size
        self.separator = separator

    def __call__(self, val):
        vals = (self.separator(val) if callable(self.separator)
                                    else val.split(self.separator))
        if self.size and len(vals) != self.size:
            msg = "Wrong number of values in {}, expected {}".format(
                vals, self.size)
            raise ValueError(msg)
        return tuple(self.converter(e) for e in vals)

class BoxParser(TupleParser):
    def __init__(self, converter=float, separator=","):
        super(BoxParser, self).__init__(converter, 4, separator)

    def __call__(self, val):
        tup = super(BoxParser, self).__call__(val)
        return ((tup[0], tup[1]), (tup[2], tup[3]))

class CircleParser(TupleParser):
    def __init__(self, converter=float, separator=","):
        super(CircleParser, self).__init__(converter, 3, separator)

    def __call__(self, val):
        tup = super(CircleParser, self).__call__(val)
        return ((tup[0], tup[1]), tup[2])

############
# Examples #
############

def test_parser(parser, value):
    try:
        tup = parser(value)
        print "{} => {}".format(value, tup)
        return tup
    except Exception as e:
        print "Failed to parse {}: {}".format(value, e)

split_strip = lambda s: [e.strip() for e in s.split(",")]

test_parser(TupleParser(int), "1,2,3")
test_parser(TupleParser(int), "1,a,3")

test_parser(TupleParser(size=3), "1,a,3")
test_parser(TupleParser(size=3), "1,a")

test_parser(TupleParser(separator=":"), "1:a:3")
test_parser(TupleParser(separator=":"), "1:a,3")

test_parser(TupleParser(separator=split_strip), "a,b,c")
test_parser(TupleParser(separator=split_strip), "a, b, c")

test_parser(BoxParser(), "1,2,3,4")
test_parser(CircleParser(), "1,2,3")

test_parser(BoxParser(Decimal), "1,2,3,4")
test_parser(CircleParser(Decimal), "1,2,3")