What error were you seeing? I would expect without `str` to also work. (Though adding it doesn't hurt, unless it's unicode)

```
In [1]: from path import path

In [2]: from omero.rtypes import *

In [3]: rstring(path("."))
Out[3]:
object #0 (::omero::RString)
{
    _val = .
}

In [4]: rstring(path(".").abspath())
Out[4]:
object #0 (::omero::RString)
{
    _val = /Users/moore
}
```