df = df.reset_index(drop=True)
>>> df.reset_index(drop=True)
class max_speed
0 bird 389.0
1 bird 24.0
2 mammal 80.5
3 mammal NaN
df.set_index('id', inplace=True)
df.to_csv(filename, index=False)
new_series = series.drop(list_of_indexes_to_be_dropped);