The GetLInearAccess functions and the objects they return rely heavily on pointer arithmetics - a concept that is not commonly used in Python and therefore not very widespread - and at the same time dangerous if not used properly as it is extremely easy to create hard-to-debug problems with it. For those reasons the linear access functions were never mapped in CVBpy.
Instead we rely on numpy arrays: The method cvb.asArray will generate a numpy view on a 
image’s pixel data (without actually copying the data) and thereby provide simple access to the pixel data in an entirely pythonic way.
If you’re interested @Andreas has written a small post about that a while ago that might be worth looking at: https://forum.commonvisionblox.com/t/getting-started-with-cvbpy/241/9