df = pd.DataFrame([[1]], columns=['col'], index=["index"])
df["col"]["index"] == df["col"][0]

df = pd.DataFrame([[1]], columns=['col'], index=[1])
# df["col"][0]  # keyerror
df["col"].iloc[0]  # 保险
df["col"].values[0] # series.values[0]
df.values[0][0]  # df.values[行][列]