[MacPorts] #67055: python portgroup overwrites PYTHONPATH in test.env

[MacPorts]

#67055: python portgroup overwrites PYTHONPATH in test.env
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  Reporter:  dgilman  |      Owner:  reneeotten
      Type:  defect   |     Status:  assigned
  Priority:  Normal   |  Milestone:
 Component:  ports    |    Version:
Resolution:           |   Keywords:
      Port:           |
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Comment (by jmroot):

 If a *.env option is set to something like `FOO=a FOO=b`, the actual FOO
 environment variable will be set to each value in succession, so
 effectively only the last occurrence of each variable counts. Since the
 portgroup is adding its value in pre-test, it will usually be the one that
 counts, and so it must be setting an empty value in this particular case.

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Ticket URL: <https://trac.macports.org/ticket/67055#comment:3>
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