Copy in python

I need an help in python script.I need to incorporate a small code in python

copy the direcotry content to other direcotry.
In my script source and destination direcotry is defined and but I don't know how to use those variabless

A=/mnt/projects
B=/mnt/projects/destination

like A is a source direcoty and B is destination diresctory
Now I don't know how to use these source and destination directory
and copy the contents of A into B directory.

look into this docs