python csv, writing headers only once

Question

So I have a program that creates CSV from .Json.

First I load the json file.

f = open('Data.json')
data = json.load(f)
f.close()

Then I go through it, looking for a specific keyword, if I find that keyword. I'll write everything related to that in a .csv file.

for item in data:
    if "light" in item:
       write_light_csv('light.csv', item)

This is my write_light_csv function :

def write_light_csv(filename,dic):

    with open (filename,'a') as csvfile:
        headers = ['TimeStamp', 'light','Proximity']
        writer = csv.DictWriter(csvfile, delimiter=',', lineterminator='
',fieldnames=headers)

        writer.writeheader()

        writer.writerow({'TimeStamp': dic['ts'], 'light' : dic['light'],'Proximity' : dic['prox']})

I initially had wb+ as the mode, but that cleared everything each time the file was opened for writing. I replaced that with a and now every time it writes, it adds a header. How do I make sure that header is only written once?.

Answer 1

You could check if file is already exists and then don't call writeheader() since you're opening the file with an append option.

Something like that:

import os.path


file_exists = os.path.isfile(filename)

with open (filename, 'a') as csvfile:
    headers = ['TimeStamp', 'light', 'Proximity']
    writer = csv.DictWriter(csvfile, delimiter=',', lineterminator='
',fieldnames=headers)

    if not file_exists:
        writer.writeheader()  # file doesn't exist yet, write a header

    writer.writerow({'TimeStamp': dic['ts'], 'light': dic['light'], 'Proximity': dic['prox']})