用datetime64[ns]用.loc（时区感知）索引DataFrame或Series是否有问题？
以下内容在最后一条语句中发出警告：
import numpy as np
import pandas as pd
N = 12
price = np.random.uniform(0, 100, N)
color = np.repeat(list("ABCD"), 3)
df = pd.DataFrame(dict(price=price, color=color),
index=pd.date_range("2020-01-01", periods=N,
freq="100ms", tz="UTC"))
df["color"] = df["color"].astype("category")
price_grp = df["price"].groupby(df["color"])
color_idxmax = price_grp.idxmax()
df_sub = df.loc[color_idxmax]
/usr/lib/python3/dist-packages/pandas/core/common.py:250: FutureWarning: Converting timezone-aware DatetimeArray to timezone-naive ndarray with 'datetime64[ns]' dtype. In the future, this will return an ndarray with 'object' dtype where each element is a 'pandas.Timestamp' with the correct 'tz'.
To accept the future behavior, pass 'dtype=object'.
To keep the old behavior, pass 'dtype="datetime64[ns]"'.
result = np.asarray(values, dtype=dtype)
INSTALLED VERSIONS
------------------
commit : None
python : 3.8.3.final.0
python-bits : 64
OS : Linux
OS-release : 5.6.0-2-amd64
machine : x86_64
processor :
byteorder : little
LC_ALL : None
LANG : en_CA.UTF-8
LOCALE : en_CA.UTF-8
pandas : 0.25.32
numpy : 1.18.4
pytz : 2020.1
dateutil : 2.8.1
pip : 20.1.1
setuptools : 46.1.3
Cython : None
pytest : 4.6.11
hypothesis : 5.16.0
sphinx : 2.4.3
blosc : 1.8.1
feather : None
xlsxwriter : None
lxml.etree : 4.5.0
html5lib : 1.0.1
pymysql : None
psycopg2 : 2.8.5 (dt dec pq3 ext lo64)
jinja2 : 2.11.2
IPython : 7.15.0
pandas_datareader: None
bs4 : 4.9.1
bottleneck : 1.2.1
fastparquet : None
gcsfs : None
lxml.etree : 4.5.0
matplotlib : 3.2.2
numexpr : 2.7.1
odfpy : None
openpyxl : 3.0.3
pandas_gbq : None
pyarrow : None
pytables : None
s3fs : None
scipy : 1.4.1
sqlalchemy : 1.3.15
tables : 3.6.1
xarray : 0.15.1
xlrd : 1.1.0
xlwt : 1.3.0
xlsxwriter : None