[GHC] #12934: Testsuite driver buffering behavior has changed with Python 3

[GHC]

#12934: Testsuite driver buffering behavior has changed with Python 3
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           Reporter:  bgamari        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.2.1
          Component:  Test Suite     |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The buffering behavior of the testsuite driver has changed with the move
 to Python 3 (#9184). Now output seems to arrive at the terminal in blocks.
 This is strange since the documentation for `sys.stdout` in Python 3.5
 claims,

 > When interactive, standard streams are line-buffered. Otherwise, they
 are    block-buffered like regular text files. You can override this value
 with the `-u` command-line option.

 It would be good to understand why this is the case.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12934>
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