[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:  1.11.0
    Component:  packaging  |    Version:  1.10.2
   Resolution:             |   Keywords:  twisted cryptography
Launchpad Bug:             |
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Comment (by warner):

 Oops, the `twisted[conch]` triggered an inclusion of `gmpy`, which fails
 to build on most systems (because they lack the `libgmp` headers). It
 turns out that `gmpy` is pretty optional: the twisted code (specifically
 `twisted/conch/ssh/common.py`) uses it to monkey-patch the built-in
 `pow()` function with a faster version. (Maybe this is old? I thought
 python used libgmp for `pow()` already). If conch cannot import `gmpy`, it
 silently continues with the default `pow()`.

 So we're reducing the dependency to just `twisted[tls]`, which currently
 gets us everything that `twisted[conch]` would get *except* for `gmpy`.
 And since `gmpy` is really optional, SFTP should still just work.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2740#comment:6>
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