import csv 
with open('ejemplo.csv', 'w') as csvfile:
   fieldnames = ['filtro1', 'filtro2', 'filtro3']
   writer  = csv.DictWriter(csvfile, fieldnames = fieldnames)
   writer.writeheader()
   writer.writerow({'filtro1' : 'Marta','filtro2' : 'Marco', 'filtro3' : 'Marso'})

print("datos insertados")

import csv
with open('ejemplo.csv') as File:
    reader = csv.reader(File, delimiter=',', quotechar=',',
                        quoting=csv.QUOTE_MINIMAL)
    for row in reader:
        print(row)

import pandas as pd 

df = pd.read_csv("ejemplo.csv") 
df.loc[0, 'filtro1'] = 'Sandra'
df.to_csv("ejemplo.csv", index=False) 
print(df)