python pathlib operator '/' - how does it do it?

Question

I found the pathlib syntax - or is it the Python syntax - surprising. I'd like to know how this makes the forward slash / act as a joiner of WindowsPath s etc. Does it override/overload / ? It seems to be in a magical context, the slash is between a WindowsPath type object and a string. If I try between 2 strings it fails to join the 2 strings (eg "123" / "123" fails)

p=pathlib.Path(".")

p
Out[66]: WindowsPath('.')

p.cwd()
Out[67]: WindowsPath('C:/Users/user1')

p.cwd() / "mydir"
Out[68]: WindowsPath('C:/Users/user1/mydir')

Answer 1

The Path class has a __truediv__ method that returns another Path. You can do the same with your own classes:

>>> class WeirdThing(object):
        def __truediv__(self, other):
            return 'Division!'

>>> WeirdThing() / WeirdThing()
'Division!'

Answer 2

For whoever wants to see the source code briefly:

__truediv__ overload the / operator, and returns self , which is a Path object.

    # this is where the magic begins! (overload the '/' operator)
    def __truediv__(self, key): 
        try:
            return self._make_child((key,))
        except TypeError:
            return NotImplemented


    def _make_child(self, args):
        drv, root, parts = self._parse_args(args)
        drv, root, parts = self._flavour.join_parsed_parts(
            self._drv, self._root, self._parts, drv, root, parts)
        return self._from_parsed_parts(drv, root, parts)


    @classmethod
    def _from_parsed_parts(cls, drv, root, parts):
        self = object.__new__(cls)
        self._drv = drv
        self._root = root
        self._parts = parts
        return self  # finally return 'self', which is a Path object.