从Bigquery存储API (python)读取数据时，如何获取“Bytes processed”和“Bytes billed”

from google.cloud import bigquery_storage_v1beta1
from google.cloud.bigquery_storage_v1beta1 import StorageClient, ReadSession, TableReadOptions

# 初始化客户端
client = StorageClient()

# 创建读取会话
session = client.create_read_session(
    parent="projects/{project_id}/datasets/{dataset_id}/tables/{table_id}",
    table_reference=table_ref,
    read_options=TableReadOptions(format_=bigquery_storage_v1beta1.types.TableModifiers(format_="AVRO"))
)

# 获取读取器
reader = session.read_rows()

# 读取数据并获取统计信息
bytes_processed = 0
bytes_billed = 0

for row in reader:
    bytes_processed += len(row)
    bytes_billed += len(row) * session.total_bytes_billed_per_row

print(f"Bytes processed: {bytes_processed}")
print(f"Bytes billed: {bytes_billed}")