def _decompose_ring_system_atom_keys(rsy):
""" decompose a ring system into a ring and a series of arcs
"""
# sort from smallest to largest
rngs_pool = sorted(rings(rsy),
key=lambda x: atom_count(x, with_implicit=False))
decomp = ()
decomp_bnd_keys = set({})
rng = rngs_pool.pop(0)
bnd_keys = bond_keys(rng)
atm_keys = sorted_ring_atom_keys_from_bond_keys(bnd_keys)
decomp += (atm_keys, )
decomp_bnd_keys.update(bnd_keys)
while rngs_pool:
decomp_rsy = bond_induced_subgraph(rsy, decomp_bnd_keys)
for idx, rng in enumerate(rngs_pool):
arcs = ring_arc_complement_atom_keys(decomp_rsy, rng)
if arcs:
rngs_pool.pop(idx)
decomp += arcs
decomp_bnd_keys.update(bond_keys(rng))
return decomp
def rings(gra):
""" rings in the graph (minimal basis)
"""
gras = [
bond_induced_subgraph(gra, bnd_keys)
for bnd_keys in rings_bond_keys(gra)
]
return tuple(sorted(gras, key=frozen))
def ring_systems(gra):
""" polycyclic ring systems in the graph
"""
gras = [
bond_induced_subgraph(gra, bnd_keys, stereo=True)
for bnd_keys in ring_systems_bond_keys(gra)
]
return tuple(sorted(gras, key=frozen))
def branch(gra, atm_key, bnd_key):
""" branch extending along `bnd_key` away from `atm_key`
"""
return bond_induced_subgraph(gra,
branch_bond_keys(gra, atm_key, bnd_key),
stereo=True)