Doubled backslashes in Windows paths

[Ned Batchelder]

On Friday, October 7, 2016 at 8:39:55 AM UTC-4, BartC wrote:
> On 07/10/2016 06:30, Oz-in-DFW wrote:
> > I'm using Python 3.5.2 (v3.5.2:4def2a2901a5, Jun 25 2016, 22:01:18) [MSC
> > v.1900 32 bit (Intel)] on Windows 7
> >
> > I'm trying to write some file processing that looks at file size,
> > extensions, and several other things and I'm having trouble getting a
> > reliably usable path to files.
> >
> > The problem *seems* to be doubled backslashes in the path, but I've read
> > elsewhere that this is just an artifact of the way the interpreter
> > displays the strings.
> >
> > I'm getting an error message on an os.path.getsize call;
> >
> >     Path: -
> >     "C:\Users\Rich\Desktop\2B_Proc\2307e60da6451986dd8d23635b845386.jpg" -
> >     Traceback (most recent call last):
> >       File "C:\Users\Rich\workspace\PyTest\test.py", line 19, in <module>
> >         if os.path.getsize(path)>10000:
> >       File "C:\Python32\lib\genericpath.py", line 49, in getsize
> >         return os.stat(filename).st_size
> >     WindowsError: [Error 123] The filename, directory name, or volume
> >     label syntax is incorrect:
> >     '"C:\\Users\\Rich\\Desktop\\2B_Proc\\2307e60da6451986dd8d23635b845386.jpg"'
> 
> I tried to recreate this error and it seems the getsize function doesn't 
> like quotes in the path.
> 
> Whether \ is correctly written as \\ in a string literal, or a raw 
> string is used with the r prefix and a single \, or a \ has been put 
> into path by any other means, then these will still be displayed as \\ 
> in the error message, which is strange. The error handler is expanding \ 
> characters to \\.

For error messages destined for developers, it is good practice to use
%r or {!r} to get the repr() of a string.  This will show quotes around
the string, and use backslash escapes to present the contents
unambiguously.  That's what's expanding \ to \\, and adding the single
quotes you see in the message.

--Ned.