text_html_output_1.png
import pandas as pd # data processing, CSV file I/O (e.g. pd.read_csv)

data = pd.read_csv('../input/air-concentration-for-the-chernobyl-disaster/data.csv')

m = data['I_131_(Bq/m3)'].str.contains('L|\\?', regex=True, na=False)
data.loc[m, 'I_131_(Bq/m3)'] = None
m = data['Cs_134_(Bq/m3)'].str.contains('N|\\?', regex=True)
data.loc[m, 'Cs_134_(Bq/m3)'] = None
m = data['Cs_137_(Bq/m3)'].str.contains('N|\\?', regex=True)
data.loc[m, 'Cs_137_(Bq/m3)'] = None

data.info()