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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 02:55:53 +0000
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Xref: csiph.com comp.lang.python:57997

> Like Victor says, that opens him up to race conditions.

Slim chance, it's no more possible than it happening in the time try/except
takes to recover an alternative procedure.

with open('in_file') as in_file, open('out_file', 'ab') as outfile_file:
    if os.path.getsize('out_file'):
        print('file not empty')
    else:
        #write header
        print('file was empty')

And if that's still not acceptable (you did say new) than open the out_file=
 'r+' an seek
and read to check for a header.

But if your file is not new and lacks a header, then what?
jlc