Numbers of Day in Month

Question

I have a data frame with a date time index, and I would like to multiply some columns with the number of days in that month.

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Answer 1

import pandas as pd
from pandas.tseries.offsets import MonthEnd

df['dim'] = (pd.to_datetime(df.index) + MonthEnd(0)).dt.day

You can omit pd.to_datetime(), if your index is already DatetimeIndex.