[tahoe-lafs-trac-stream] [Tahoe-LAFS] #2740: Twisted 16.0.0 causes test failure when importing cryptography.exceptions

[Tahoe-LAFS]

#2740: Twisted 16.0.0 causes test failure when importing cryptography.exceptions
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     Reporter:  daira      |      Owner:  daira
         Type:  defect     |     Status:  new
     Priority:  normal     |  Milestone:  undecided
    Component:  packaging  |    Version:  1.10.2
   Resolution:             |   Keywords:  twisted cryptography
Launchpad Bug:             |
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Comment (by warner):

 It looks like Twisted only declares a dependency on "cryptography" if you
 ask for the "conch" extra, as in `pip install twisted[conch]`, or
 `install_requires = [ "Twisted[conch]" ]`. The previous twisted-15.5.0 had
 a `[conch]` dependency of "gmpy, pyasn1, pycrypto", which overlapped
 enough with what Tahoe declares dependencies on that things still worked.
 Twisted-16.0.0 changed conch to "gmpy, pyasn1, cryptography".

 Tahoe has been in the practice of declaring a transitive closure of
 dependencies, and I think it's time we ended that and let pip have
 responsibility for figuring out the transitive set. (We can always add a
 `requires.txt` if we want to behave like an application, as opposed to a
 library, and also provide peep-style hashes of upstream tarballs/wheels).
 We should declare a dependency on `Twisted[conch]`. Foolscap should
 declare `Twisted[tls]` (added as
 [https://foolscap.lothar.com/trac/ticket/249 foolscap#249]).

 And I think it might be appropriate for tahoe to have a windows-
 conditional dependency on `Twisted[windows]`, since that's what triggers
 twisted to ask for `pypiwin32`.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2740#comment:1>
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