0.8.00 testsuite fails with python 3.5.3 and gnupg 2.1.18

[az]

with python 3.5.3 and gnupg 2.1.18 the testsuite repeatably fails unit/test_collections.py and almost all of unit/test_gpg.py and unit/test_gpginterface.py.

the error messages all point to the same bit of code at duplicity/gpginterface.py:447, so i'm just including the first one:

=================================== FAILURES ===================================
_____________________ CollectionTest.test_sigchain_fileobj _____________________

self = <testing.unit.test_collections.CollectionTest testMethod=test_sigchain_fileobj>

    @pytest.mark.usefixtures(u"redirect_stdin")
    def test_sigchain_fileobj(self):
        u"""Test getting signature chain fileobjs from archive_dir_path"""
> self.set_gpg_profile()

unit/test_collections.py:189:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
unit/test_collections.py:97: in set_gpg_profile
    self.set_global(u'gpg_profile', gpg.GPGProfile(passphrase=u"foobar"))
../duplicity/gpg.py:95: in __init__
    self.gpg_version = self.get_gpg_version(globals.gpg_binary)
../duplicity/gpg.py:111: in get_gpg_version
    res = gnupg.run([u"--version"], create_fhs=[u"stdout"])
../duplicity/gpginterface.py:375: in run
    create_fhs, attach_fhs)
../duplicity/gpginterface.py:427: in _attach_fork_exec
    self._as_child(process, gnupg_commands, args)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <duplicity.gpginterface.GnuPG object at 0x7fa25e8e52b0>
process = <duplicity.gpginterface.Process object at 0x7fa25f64cc88>
gnupg_commands = ['--version'], args = []

    def _as_child(self, process, gnupg_commands, args):
        u"""Stuff run after forking in child"""
        # child
        for std in _stds:
            p = process._pipes[std]
> os.dup2(p.child, getattr(sys, u"__%s__" % std).fileno())
E ValueError: underlying buffer has been detached

../duplicity/gpginterface.py:447: ValueError

with python 3.7.3 and gnupg 2.2.12 or 2.2.13 those same tests survive just fine.