Gotha,wait a moment,I'm writing it.
This code is written according to the cases you just described
the APath and BPath should be the path of A and B folder.
#
import tarfile
import os
APath = 'A'
dirA = os.walk(APath).next()[2]
tarA = tarfile.open('A/txt.tar.bz','w:bz2')
for file in dirA:
tarA.add(os.path.join(APath,file))
tarA.close()
BPath = 'B'
dirB = os.walk(BPath).next()[1]
os.chdir('B')
for directory in dirB:
tar = tarfile.open(directory+'tar.bz','w:bz2')
tar.add(directory)
tar.close()