file_move_safe doesn't respect it's docstring

[Ioan Alexandru Cucu]

django.core.files.move.file_move_safe's docstring states the following:

If the destination file exists and allow_overwrite is False, this
function will throw an IOError.

However, if the destination file exists and movement is performed using os.rename (which is the case most of the times) then no exception is being thrown. The exception is only being thrown if streaming manually from one file to another.

This could be fixed by doing one of the following:

1. update the docstring to match the actual behavior
2. make the function raise IOError regardless of how the movement is being performed

[Ioan Alexandru Cucu]

Note. This might be platform dependent.
I reproduced this on Linux 3.2.0-23-generic-pae #36-Ubuntu SMP

[Kamu]

Looking over the code and ​http://docs.python.org/2/library/os.html#os.rename it looks like this is quite true.

An interesting note is os.rename will not replace the file on Windows: "On Windows, if dst already exists, OSError will be raised even if it is a file; there may be no way to implement an atomic rename when dst names an existing file." So this seems to be unix systems only.

[Kamu]

I had a stab at fixing it. Please see:

​https://github.com/django/django/pull/1253

[Russell Keith-Magee <russell@…>]

In 18e79f1425fa87f2f38df25c65203ec4d311f499:

Fixed #20486 -- Ensure that file_move_safe raises an error if the destination already exists.

Thanks to kux for the report, and Russ Webber for the patch.