How to convert one coordinate value (Y) to world coordinate ?

I just need to convert one value, its vertex Y location of object. I have looked many examples but I dont get it.

You just have to multiplicate the world matrix by the local coordinate.
For example

import bpy
obj = bpy.context.active_object
wmtx = obj.matrix_world
for face in obj.data.polygons:
for vert in face.vertices:
vertex = wmtx * obj.data.vertices[vert].co
print(“vertex global %s” % vertex)

How do I get the world coordinates of a control vertex of a BezierCurve?
http://wiki.blender.org/index.php/Doc:2.6/Manual/Extensions/Python/FAQ

Thank you. So I need all this stuff to calculate one vertex y-coordinate to world coordinates ? I know that vertex index number also.

Eidt: yes, I have read that article also, I still dont get it how to calculate one (1) value to world coordinate.

no if you know the vertex index, for example say is 36, and just want Y

v = wmtx * obj.data.vertices[36].co
print (“Y: %s” % v[1])

okey, thanks, I’ll try that.