Infers standard paths to policy and model directories.

  Example:
    >>> infer_paths("/some/output/dir/", policy="", model="custom/path")
    {"policy": "/some/output/dir/policy", "model": "custom/path",
    "output_dir":"/some/output/dir/"}

  Args:
    output_dir: output directory.
    **subdirs: sub-directories.

  Returns:
    a dictionary with the directories.

def infer_paths(output_dir, **subdirs):
  """Infers standard paths to policy and model directories.

  Example:
    >>> infer_paths("/some/output/dir/", policy="", model="custom/path")
    {"policy": "/some/output/dir/policy", "model": "custom/path",
    "output_dir":"/some/output/dir/"}

  Args:
    output_dir: output directory.
    **subdirs: sub-directories.

  Returns:
    a dictionary with the directories.
  """
  directories = {}
  for name, path in six.iteritems(subdirs):
    directories[name] = path if path else os.path.join(output_dir, name)
  directories["output_dir"] = output_dir
  return directories