Getting a vector from two objects.

import maya.OpenMaya as om

import maya.cmds as cmds

# I named both my objects in maya scene 'tgt' and 'src' repsectively. tgtObj= 'tgt'

aimObj = 'src'

# definition for a worldSpacePosition matrix.

def getWorldPos( object ):

# utils needed to be imported for converting from a list to a matrix product.

util = om.MScriptUtil()

xform = cmds.xform( object, ws=1, m=1, q=1 )

# the 16 is the length of numbers in list. Specifically, a Matrix.

util.createFromList( xform, 16 )

return om.MMatrix( util.asFloat4Ptr() )

# get the worldSpacePosition of both objects.

aimM = getWorldPos( aimObj )

tgtM = getWorldPos( tgtObj )

# gets a pointMatrix product.

aimOrig = om.MPoint(0.0,0.0,0.0)

tgtOrig = om.MPoint(0.0,0.0,0.0)

aimOrig *= getWorldPos( aimObj )

tgtOrig *= getWorldPos( tgtObj )

#v = aimOrig * aimM.transpose()

#print v.x, v.y, v.z

print aimOrig.x, aimOrig.y, aimOrig.z

v = aimOrig - tgtOrig

print v.x, v.y, v.z