using dir_fd=None in some functions

[Larz60+]

Use try/except block

with os imported:

>>> import os
>>> os.supports_dir_fd
{<built-in function mknod>, <built-in function open>, <built-in function symlink>, <built-in function access>, <built-in function chown>, <built-in function mkfifo>, <built-in function readlink>, <built-in function rename>, <built-in function rmdir>, <built-in function utime>, <built-in function link>, <built-in function mkdir>, <built-in function unlink>, <built-in function chmod>, <built-in function stat>}
>>>

without os imported:

>>> try:
...     os.supports_dir_fd
... except NameError:
...     print("Did You forgot to import os?")
... 
Did You forgot to import os?
>>>