Path.with_name can be used to construct paths containing slashes as name contents (rather than as separators), as demonstrated below.

$ python -c 'from pathlib import Path; print(Path("foo").with_name("bar/baz").name)'
bar/baz

This should be changed to either raise a ValueError, or behave like path.parent / new_name.  Given the amount of checking in the related with_suffix method (and the fact that the second option can be readily implemented by hand), the first option seems preferable.

I think raising ValueError is the way to go. Would you like to try writing a patch for it?

I have the patch almost ready, but ran into another issue: should "path.with_name('foo/')" be allowed?  It may make sense to treat it like "path.with_name('foo')", just like 'Path("foo/") == Path("foo")'.

The implementation is also simpler with it, as it can reuse the "parse_parts" approach used by "with_suffix".  But this also raises a separate issue, which is that with the current implementation, we have "Path('foo').with_suffix('.bar') == Path('foo').with_suffix('.bar/')", and that is less reasonable.  Should I open a separate issue for that?

> should "path.with_name('foo/')" be allowed?

For sanity, I think path separators should be disallowed.

The attached patch fixes all the issues mentioned, and also integrates the fixes of issue 20639 (issues with with_suffix) as they are quite similar.

New changeset c2636b5816a3 by Antoine Pitrou in branch '3.4':
Issue #21714: Disallow the construction of invalid paths using Path.with_name().  Original patch by Antony Lee.
http://hg.python.org/cpython/rev/c2636b5816a3

Ok, patch now applied (as well as the original patch for with_suffix()). Thank you very much!