'Create an Opener.
Args:
filename: string, The pathname of the file.
mode: string, The preferred mode to access the file with.
fallback_mode: string, The mode to use if locking fails.'

def __init__(self, filename, mode, fallback_mode):

    self._locked = False
    self._filename = filename
    self._mode = mode
    self._fallback_mode = fallback_mode
    self._fh = None
