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Removing Non ASCII characters and replacing with spaces from Pandas data frame
Which tells how to remove non ASCII characters from Pandas columns
df['DB_user'] = df["DB_user"].apply(lambda x: ''.join([" " if ord(i) < 32 or ord(i) > 126 else i for i in x]))
From the UTF-8 wikipedia, UTF-8 is
The first 128 characters of Unicode
https://en.wikipedia.org/wiki/UTF-8
So my guess is that the solution would be
df['DB_user'] = df["DB_user"].apply(lambda x: ''.join([" " if ord(i) > 127 else i for i in x]))