Suppose code:
=====================================
import os
import tempfile

want_to_replace = 'zxc.dat'
tmpdir=os.path.dirname(os.path.realpath(want_to_replace))
with tempfile.NamedTemporaryFile(dir=tmpdir) as fff:
    # do somewhat with fff here... and then:
    fff.flush()
    os.fdatasync(fff)
    os.rename(fff.name, want_to_replace)
    fff.delete = False
=====================================
In python 3.3 and lower that works FINE. In Python 3.4 the fff._closer attribute was introduced, so fff.close=False stopped to work. I think this is major loss of functionality. The "close" attribute was not marked as private, so may be used in past.