how to add headers in csv file using python

import csv

f = open("fruits.csv", "w")
writer = csv.DictWriter(
    f, fieldnames=["fruit", "count"])
writer.writeheader()
f.close()
Outputfruits.csvfruit,count

   from pandas import read_csv

   df = read_csv('test.csv')
   df.columns = ['a', 'b']
   df.to_csv('test_2.csv')

#header in csv file
import pandas as pd
import csv
df = pd.read_csv("file.csv", header=None)
df.to_csv("file.csv", header=["SEQUENCE"], index=False)#header added
df = pd.read_csv("file.csv")
df