Marko Rauhamaa wrote:
> Chris Angelico <ros...@gmail.com>:
>
> > Marko Rauhamaa <ma...@pacujo.net> wrote:
> >>
> >> This surprising exception can even be a security issue:
> >>
> >> >>> os.path.exists("\0")
> >> Traceback (most recent call last):
> >> File "<stdin>", line 1, in <module>
> >> File "/usr/lib64/python3.6/genericpath.py", line 19, in exists
> >> os.stat(path)
> >> ValueError: embedded null byte
> >
> > [...]
> >
> > A Unix path name cannot contain a null byte, so what you
> > have is a fundamentally invalid name. ValueError is
> > perfectly acceptable.
>
> At the very least, that should be emphasized in the
> documentation. The pathname may come from an external
> source. It is routine to check for "/", "." and ".." but
> most developers (!?) would not think of checking for "\0".
> That means few test suites would catch this issue and few
> developers would think of catching ValueError here. The end
> result is unpredictable.
I'd have to agree with this assessment. Either a filepath
exists, or it doesn't. Therefore, in the "worldview" of
os.path.exist, there should be no consideration of
conformity, as it is blatantly obvious that any malformed
path would _not_ and could _not_ possibly, exist. In fact,
the only case in which the method in question should raise
an Exception is when a non-stringy argument is passed. Which
-- at least in 2.x version -- i can confirm (with limited
testing) it does this correctly!
## PYTHON 2.X SESSION ##
py> os.path.exists('')
False
py> os.path.exists(None)
Traceback (most recent call last):
File "<pyshell#5>", line 1, in <module>
os.path.exists(None)
File "C:\Python27\lib\genericpath.py", line 26, in exists
os.stat(path)
TypeError: coercing to Unicode: need string or buffer, NoneType found
>>> os.path.exists(1)
Traceback (most recent call last):
File "<pyshell#6>", line 1, in <module>
os.path.exists(1)
File "C:\Python27\lib\genericpath.py", line 26, in exists
os.stat(path)
TypeError: coercing to Unicode: need string or buffer, int found
But if the argument is a string, either it exists as a
filepath or it doesn't. Case closed. Anything less would
constitute type discrimination. Which is not only
inconsistent, it's unethical.
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