Notes

// Assume we have a 'gender' column with only M and F values
// solution 1
users['gender_n'] = [1 if gender == 'M' else 0 for gender in users['gender']]

// solution 2
users['gender_n'] = np.where(users['gender'] == 'M', 1, 0)

// solution 3
users['gender_n'] = (users['gender'] == 'M').astype(int)