Using "with open(filename, 'ab'):" and calling code only if the file is new?

[Victor Hooi]

Hi,

I have a CSV file that I will repeatedly appending to.

I'm using the following to open the file:

    with open(self.full_path, 'r') as input, open(self.output_csv, 'ab') as output:
        fieldnames = (...)
        csv_writer = DictWriter(output, filednames)
        # Call csv_writer.writeheader() if file is new.
        csv_writer.writerows(my_dict)

I'm wondering what's the best way of calling writeheader() only if the file is new?

My understanding is that I don't want to use os.path.exist(), since that opens me up to race conditions.

I'm guessing I can't use try-except with IOError, since the open(..., 'ab') will work whether the file exists or not.

Is there another way I can execute code only if the file is new?

Cheers,
Victor