I have a question about Python data coupling.

import pandas as pd

pd.set_option('display.unicode.east_asian_width', True)

series = pd.Series(
  ['1/1', '1/2', '1/3', '1/4', '1/5', '1/6', '1/7', '1/8', '1/9', '1/10'],
  name = 'Date')

df1 = pd.DataFrame({
  'Date': ['1/1', '1/2', '1/3', '1/4', '1/5', '1/6', '1/7',
  Weather: ['Clear', 'Clear', 'Cloudy', 'Clear', 'Clear', 'Clear', 'Clear', 'Clear', 'Clear',
})

dfx=pd.merge(series, df1, on='date', how='left')
# dfx = df1.set_index('date') .reindex(series).reset_index()
print(dfx)

#
   date weather
01/1 Clear
1/2. Clear
2 1/3 Cloudy
3 1/4 sunny
41/5 Cloudy
51/6 Cloudy
6 1/7 Clear
7 1/8 NaN
81/9 NaN
91/10 NaN