if you want all the bond lengths within the unit cell, then you can do this by instantiating the crystal's molecule and measuring the the distances between the bonds' atoms. For example,
from ccdc import io, descriptors
csd = io.EntryReader('csd')
crystal = csd.crystal('AABHTZ')
mol = crystal.molecule
for b in mol.bonds:
print('%s-%s: %.2f' % (b.atoms, b.atoms, descriptors.MolecularDescriptors.atom_distance(b.atoms, b.atoms)))
Please let me know if I have misunderstood your problem.