It seems there is a sporadic failure on OS X (oops, sorry, I mean "macOS"):
https://travis-ci.org/python/cpython/jobs/248079407#L3403
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FAIL: test_getsitepackages (test.test_site.HelperFunctionsTests)
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Traceback (most recent call last):
File "/Users/travis/build/python/cpython/Lib/test/test_site.py", line 266, in test_getsitepackages
self.assertEqual(len(dirs), 2)
AssertionError: 1 != 2
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