要合并两个 Dataframe ，必须找到一个公共键。您可以从第二个 Dataframe 的Date列中提取年份。现在，您有一个用于处理内部连接的公共键：

# If needed, convert date_time as datetime64
weather['date_time'] = pd.to_datetime(weather['date_time'])

# If needed, convert Date as int
cleaned['Date'] = cleaned['Date'].astype(int)

out = cleaned.merge(weather.assign(Date=df2['datetime'].dt.year), on='Date')

您需要从'date_time'创建一个新列，其中只包含year，然后对'Year'列应用合并。在那之后，如果你不想在你的数据框中保留日期时间列。

weather['date_time'] = pd.to_datetime(df['date_time'])
weather['Date'] = weather['date_time'].dt.year

combined = cleaned.merge(weather, on = 'Date')

# after that drop the 'date_time' column

combined.drop(['date_time'], axis = 1, inplace = True)