def get_attestation_participants(state: 'BeaconState',
slot: int,
shard: int,
participation_bitfield: bytes,
epoch_length: int) -> Iterable[int]:
"""
Return the participants' indices at the ``slot`` of shard ``shard``
from ``participation_bitfield``.
"""
# Find the relevant committee
# Filter by slot
shard_committees_at_slot = get_shard_committees_at_slot(
state,
slot,
epoch_length,
)
# Filter by shard
shard_committees = tuple(
[
shard_committee
for shard_committee in shard_committees_at_slot
if shard_committee.shard == shard
]
)
try:
shard_committee = shard_committees[0]
except IndexError:
raise ValidationError("shard_committees should not be empty.")
if len(participation_bitfield) != get_bitfield_length(len(shard_committee.committee)):
raise ValidationError(
'Invalid bitfield length,'
"\texpected: %s, found: %s" % (
get_bitfield_length(len(shard_committee.committee)),
len(participation_bitfield),
)
)
# Find the participating attesters in the committee
for bitfield_index, validator_index in enumerate(shard_committee.committee):
if has_voted(participation_bitfield, bitfield_index):
yield validator_index
def test_bitfield_length(attester_count, bitfield_length):
assert get_bitfield_length(attester_count) == bitfield_length