Interoperability of fspath str only version

fspath_str.py

# This is posixpath from Python 3.4 based (not ideal, but it is what I had handy)

from os.path import _get_sep


# str-only.
def fspath(path):
    try:
        path = path.__fspath__()
    except AttributeError:
        pass
    if isinstance(path, str):
        return path
    else:
        raise TypeError


# os.path.join is meaty enough to test things
def join(a, *p):
    """Join two or more pathname components, inserting '/' as needed.
    If any component is an absolute path, all previous path components
    will be discarded.  An empty last part will result in a path that
    ends with a separator."""
    if not isinstance(a, bytes):
        a = fspath(a)
    sep = _get_sep(a)
    path = a
    try:
        for b in p:
            if not isinstance(b, bytes):
                b = fspath(b)
            if b.startswith(sep):
                path = b
            elif not path or path.endswith(sep):
                path += b
            else:
                path += sep + b
    except TypeError:
        if all(isinstance(s, (str, bytes)) or hasattr(s, "__fspath__") for s 
               in (a,) + p):
            # Must have a mixture of text and binary data
            raise TypeError("Can't mix strings and bytes in path " + 
                            "components") from None
        raise
    return path


# Simple "rich path" object that just passes through its constructor (bytes or str)
class RichPath:

  def __init__(self, path):
    self.path = path

  def __fspath__(self):
   return self.path