Modification of fields

Dear all,

How far from working is the code below?
The idea is to change the field "x" to give it a new value, and to reconstruct the stream with this new value.

https://bitbucket.org/haypo/hachoir/wiki/Ideas apparently explains that it has been envisaged. I
quote: "Event driven system: allow fields to signal modify events up to parent fields, all the way to root".

Regards,
Louis

from hachoir_core.stream import StringInputStream, LITTLE_ENDIAN
from hachoir_core.field import Parser, CString, UInt16
class Point(Parser):
    endian = LITTLE_ENDIAN
    def createFields(self):
        yield CString(self, "name", "Point name")
        yield UInt16(self, "x", "X coordinate")
        yield UInt16(self, "y", "Y coordinate")

d0 = "point\0\3\0\2\0"
p0 = Point(StringInputStream(d0))
d1 = "point\0\8\0\8\0"
p1 = Point(StringInputStream(d1))

p0["x"].value
p0.replaceField("x",p1["x"])