Rename file without overwriting existing files

Wolfgang Maier wolfgang.maier at biologie.uni-freiburg.de
Mon Jan 30 06:24:58 EST 2017


On 01/30/2017 03:49 AM, Steve D'Aprano wrote:
> This code contains a Time Of Check to Time Of Use bug:
>
>     if os.path.exists(destination)
>         raise ValueError('destination already exists')
>     os.rename(oldname, destination)
>
>
> In the microsecond between checking for the existence of the destination and
> actually doing the rename, it is possible that another process may create
> the destination, resulting in data loss.
>
> Apart from keeping my fingers crossed, how should I fix this TOCTOU bug?
>

There is a rather extensive discussion of this problem (with no good 
cross-platform solution if I remember correctly):

https://mail.python.org/pipermail/python-ideas/2011-August/011131.html

which is related to http://bugs.python.org/issue12741

Wolfgang



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