[issue26798] add BLAKE2 to hashlib

[Martin Panter]

Martin Panter added the comment:

Seems the test fails if the installed Python tree is not writable:
http://buildbot.python.org/all/builders/x86%20Gentoo%20Installed%20with%20X%203.x/builds/1005/steps/test/logs/stdio
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ERROR: test_blake2b_vectors (test.test_hashlib.HashLibTestCase)
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Traceback (most recent call last):
  File "/buildbot/buildarea/3.x.ware-gentoo-x86.installed/build/target/lib/python3.6/test/test_hashlib.py", line 537, in test_blake2b_vectors
    for msg, key, md in read_vectors('blake2b'):
  File "/buildbot/buildarea/3.x.ware-gentoo-x86.installed/build/target/lib/python3.6/test/test_hashlib.py", line 50, in read_vectors
    with support.open_urlresource(URL.format(hash_name)) as f:
  File "/buildbot/buildarea/3.x.ware-gentoo-x86.installed/build/target/lib/python3.6/test/support/__init__.py", line 1061, in open_urlresource
    with open(fn, "wb") as out:
PermissionError: [Errno 13] Permission denied: '/buildbot/buildarea/3.x.ware-gentoo-x86.installed/build/target/lib/python3.6/test/data/blake2b.txt'

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ERROR: test_blake2s_vectors (test.test_hashlib.HashLibTestCase)

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue26798>
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