fillna ffill bfill

humidity = humidity.fillna(method='ffill')

 It is cleaned using fillna() method with ffill parameter which propagates last valid observation to fill gaps

.fillna(method='bfill')

First, we used ffill parameter which propagates last valid observation to fill gaps. Then we use bfill to propogate next valid observation to fill gaps.

bfill이 뒤에 걸로 앞으 Nan값을 채우겠다는 뜻.