Check if datetime column is empty

Question

I want to check inside function like if datetime column is empty do something. My sample df:

    date_dogovor    date_pogash date_pogash_posle_prodl
0   2019-03-07  2020-03-06  NaT
1   2019-02-27  2020-02-05  NaT
2   2011-10-14  2016-10-13  2019-10-13
3   2019-03-28  2020-03-06  NaT
4   2019-04-17  2020-04-06  NaT

My function:

def term(date_contract , date_paymnt, date_paymnt_aftr_prlngtn):
if date_paymnt_aftr_prlngtn is None:
    return date_paymnt - date_contract 
else:
    return date_paymnt_aftr_prlngtn - date_contract 

Applying function to df:

df['term'] = df.apply(lambda x: term(x['date_dogovor'], x['date_pogash'], x['date_pogash_posle_prodl']), axis=1 )

Result is wrong:

df['term']

    0              NaT
1              NaT
2              NaT
3              NaT
4              NaT
            ...   
115337         NaT
115338         NaT
115339   2921 days
115340         NaT
115341         NaT
Name: term, Length: 115342, dtype: timedelta64[ns]

How to correctly check if datetime column is empty?

Answer 1

Here is better/faster use numpy.where with Series.isna:

df['term'] = np.where(df['date_pogash_posle_prodl'].isna(),
                      df['date_pogash'] - df['date_dogovor'], 
                      df['date_dogovor'] - df['date_dogovor'])

Your function should be changed with pandas.isna:

def term(date_contract , date_paymnt, date_paymnt_aftr_prlngtn):
    if pd.isna(date_paymnt_aftr_prlngtn):
        return date_paymnt - date_contract 
    else:
        return date_paymnt_aftr_prlngtn - date_contract