pandas.dataframe 可以保持 ds 作为 datetime 对象，也可以进行比较 hours, minutes, seconds .
使用 .strftime() 也不会起作用，因为它可能不会比较 datetime 具有 string -但如果它能够比较它们，那么它仍然会使用 hours, minutes, seconds 对于中的值 ds .
您可能需要使用 .dt.date 对于 dataframe 及 .date() 单身 datetime 只比较日期。
最小示例

import datetime
import time

one_day = datetime.timedelta(days=1)

tomorrow_1 = datetime.datetime.today() + one_day
time.sleep(2) # to create values with different seconds
tomorrow_2 = datetime.datetime.today() + one_day

print('tomorrow_1:', tomorrow_1, '| strftime:', tomorrow_1.strftime('%Y-%m-%d'))
print('tomorrow_2:', tomorrow_2, '| strftime:', tomorrow_2.strftime('%Y-%m-%d'))

print('           dt == dt            :', tomorrow_1 == tomorrow_2)
print('           dt == dt.strftime() :', tomorrow_1 == tomorrow_2.strftime('%Y-%m-%d'))
print('dt.strftime() == dt.strftime() :', tomorrow_1.strftime('%Y-%m-%d') == tomorrow_2.strftime('%Y-%m-%d'))
print('    dt.date() == dt.date()     :', tomorrow_1.date() == tomorrow_2.date())

# ------------------------------------------

import pandas as pd

df = pd.DataFrame({
    'ds': [tomorrow_1, tomorrow_2]
})

print('\n--- dtypes ---')
print(df.dtypes)

print('\n--- selected: dt == dt ---')

selected = df[ df['ds'] == tomorrow_1 ]
print(selected)

print('\n--- selected: dt == dt.strftime() ---')

selected = df[ df['ds'] == tomorrow_1.strftime('%Y-%m-%d') ]
print(selected)

print('\n--- selected: dt.strftime() == dt.strftime() ---')

selected = df[ df['ds'].dt.strftime('%Y-%m-%d') == tomorrow_1.strftime('%Y-%m-%d') ]
print(selected)

print('\n--- selected: dt.date() == dt.date() ---')

selected = df[ df['ds'].dt.date == tomorrow_1.date() ]
print(selected)

结果:

tomorrow_1: 2021-07-11 17:31:50.259787 | strftime: 2021-07-11
tomorrow_2: 2021-07-11 17:31:52.260139 | strftime: 2021-07-11
           dt == dt            : False
           dt == dt.strftime() : False
dt.strftime() == dt.strftime() : True
    dt.date() == dt.date()     : True

--- dtypes ---
ds    datetime64[ns]
dtype: object

--- selected: dt == dt ---
                          ds
0 2021-07-11 17:31:50.259787

--- selected: dt == dt.strftime() ---
Empty DataFrame
Columns: [ds]
Index: []

--- selected: dt.strftime() == dt.strftime() ---
                          ds
0 2021-07-11 17:31:50.259787
1 2021-07-11 17:31:52.260139

--- selected: dt.date() == dt.date() ---
                          ds
0 2021-07-11 17:31:50.259787
1 2021-07-11 17:31:52.260139

编辑：
其他例子

import datetime

one_day = datetime.timedelta(days=1)

today     = datetime.datetime.today()
yesterday = today - one_day
tomorrow  = today + one_day

two_days_later = today + 2*one_day

# --- generate some data ---

import pandas as pd

forecast = pd.DataFrame({
    'ds': [yesterday, today, tomorrow, two_days_later],
    'yhat': [111, 222, 333, 444],
})

print('- forecast -')
print(forecast)

# --- find tomorrow ---

tomorrow = datetime.datetime.today() + datetime.timedelta(days=1)

mask = ( forecast['ds'].dt.date == tomorrow.date() )
print('- mask -')
print(mask)

selected = forecast[ mask ]

print('- selected -')
print(selected['yhat'].item())