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From: "Joseph L. Casale" <jcasale@activenetwerx.com>
To: "python-list@python.org" <python-list@python.org>
Subject: RE: Using "with open(filename, 'ab'):" and calling code only if the file is new?
Thread-Topic: Using "with open(filename, 'ab'):" and calling code only if the file is new?
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Date: Wed, 30 Oct 2013 01:42:50 +0000
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Xref: csiph.com comp.lang.python:57990

>     with open(self.full_path, 'r') as input, open(self.output_csv, 'ab') =
as
> output:
>         fieldnames =3D (...)
>         csv_writer =3D DictWriter(output, filednames)
>         # Call csv_writer.writeheader() if file is new.
>         csv_writer.writerows(my_dict)
>=20
> I'm wondering what's the best way of calling writeheader() only if the fi=
le is
> new?
>=20
> My understanding is that I don't want to use os.path.exist(), since that =
opens
> me up to race conditions.

What stops you from checking before and setting a flag?