import pandas as pd
import numpy as np

from io import StringIO
source = StringIO('[{"drop_id":101,"kg":12},{"drop_id":102,"kg":8}]')
table = pd.read_json(source, orient="records", dtype={"drop_id":"int64", "kg":"float64"})
print(table["drop_id"].tolist())
print(float(table["kg"].sum()))
print(table["kg"].dtype.name)