# import necessary libraries
import pandas as pd
import re
# create a sample pandas series
emails = pd.Series(['[email protected]', 'invalid email', \
'fake_email.com', '[email protected]'])
# define regex pattern
pattern = r'[a-zA-Z0-9._%+-][email protected][a-zA-Z0-9.-]+\.[a-zA-Z]{2,}'
# find valid emails using findall()
result_emails = emails.str.findall(pattern, flags=re.IGNORECASE)
# remove invalid ones from the result
valid_emails = result_emails.apply(lambda x: x[0] if len(x) > 0
else float('NaN'))
# print results
print(valid_emails.dropna())