Python - eliminating a certain data from strings. how do I drop those values without dropping whole column?

[Katherineamt]

New in Python. I have strings of info and in some rows of few columns 'nan' value shows up because a cell in excel is empty (and it should be empty). Question: how do I drop those values without dropping whole column?

#excel file and my desired output:
n1 b1 n2 b2
1 2
1 2
1 2 3 4
1 2 3 4
What i get:
n1 b1 n2 b2
1 2 'nan' 'nan'
1 2 'nan' 'nan'
1 2 3 4
1 2 3 4
what I have so far

for k in range(len(switched_shunt_data['I'])):
    f.write('{:>6},'.format(str(switched_shunt_data['N1'][k]).encode('utf-8')) + \
            '{:>2},'.format(switched_shunt_data['N1'][k]) + \
            '{:>8},'.format(switched_shunt_data['B1'][k]) + \
            if switched_shunt_data['N2'][k] == 'nan':
                .drop(switched_shunt_data['N2'][k])
            else:
                '{:>2},'.format(switched_shunt_data['N2'][k])
            '{:>8},'.format(switched_shunt_data['B2'][k]) + '\n')

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Модератор

[Black Fregat]

from math import isnan
if isnan(switched_shunt_data['N2'][k]):