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='\n',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='\n',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']}) 

Answer 2

Just another way:

with open(file_path, 'a') as file:         w = csv.DictWriter(file, my_dict.keys())          if file.tell() == 0:             w.writeheader()          w.writerow(my_dict)