It would be great if we could "add" either str or Path to Path objects.  Currently, we can join paths only by adding a directory, or by replacing the suffix.  But sometimes we want to build up a path more directly.  With strings we can do that simply by concatenating strings.  It would be great if we could do the same with Path objects, like this:

In [2]: b = pathlib.Path("/tmp/some_base")

In [3]: b + "_name.dat"
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-939467ea0aa5> in <module>()
----> 1 b + "_name.dat"

TypeError: unsupported operand type(s) for +: 'PosixPath' and 'str'

In [4]: b + pathlib.Path("_name.dat")
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-460bf8ac7710> in <module>()
----> 1 b + pathlib.Path("_name.dat")

TypeError: unsupported operand type(s) for +: 'PosixPath' and 'PosixPath'

In [11]: b.with_name(b.name + "_name.dat")  # desired effect
Out[11]: PosixPath('/tmp/some_base_name.dat')

I would expect addition to return PosixPath('/tmp/some_base/_name.dat'), (ie: path.join).

I agree with David. And, it already works, but uses '/', not '+':

>>> b / "_name.dat"
PosixPath('/tmp/some_base/_name.dat')

-1 to using + to be the equivalent of:

>>> pathlib.Path(str(b) + "_name.dat")
PosixPath('/tmp/some_base_name.dat')

Indeed, not trying to pretend to act like a string was one of the design points of the pathlib module, and the "/" operator already performs logical path joining. I'm therefore closing this issue as rejected.