Blender 2.8 (python) - how do I get the vector of the direction the camera points In python, how do I calculate/find/retrieve the XYZ vector from the location of the camera and through the midpoint of the camera view?

In the example below the camera is at location (7.4, -6.9, 5.0) and points at the origin (0,0,0); therefore the vector should be (-7.4, +6.9, -5.0)

I suspect the camera's location and rotation parameters hold the answer, but the I can't figure out the calculations.  For example, in moving the origin there is clearly movement along the Y axis, but the rotation on the Y-axis is zero so I don't know how to do it.
Since a clear rotation camera (0,0,0) point down z-axis.

So the vector should be $camera\ rotation\ matrix\times Vector(0,0,-1)$

In code:

v = Vector((0,0,-1)) #Down vector
v.rotate(camera.rotation_euler)

v #this vector



  Except
  
  Keep in mind that camera can have another transform by parent offset and some other modifier. If the camera rotation is not pure, you will need to apply the transform to that rotation as well.