The test in setup.py to check for SSE2 support is incorrect.  Checking that arch == x86_64 is not sufficient.  If the kernel is 64-bit but Python is compiled with a 32-bit compiler, the _blake2 module will fail to build.

The attached patch fixes this issue. I did a quick search of the x86_64 string, I don't see this mistake being made elsewhere but I imagine it could be done elsewhere.  Obviously a machine with a 64-bit kernel and 32-bit userspace is a rare as hen's teeth these days.  Still, I think it is worth fixing this bug.

Python 3.6.1 (default, Apr 27 2017, 20:09:03) 
[GCC 4.9.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import hashlib
ERROR:root:code for hash blake2b was not found.
Traceback (most recent call last):
  File "/home/nas/PPython-3.6.1/Lib/hashlib.py", line 243, in <module>
    globals()[__func_name] = __get_hash(__func_name)
  File "/home/nas/PPython-3.6.1/Lib/hashlib.py", line 119, in __get_openssl_constructor
    return __get_builtin_constructor(name)
  File "/home/nas/PPython-3.6.1/Lib/hashlib.py", line 113, in __get_builtin_constructor
    raise ValueError('unsupported hash type ' + name)
ValueError: unsupported hash type blake2b
ERROR:root:code for hash blake2s was not found.
Traceback (most recent call last):
  File "/home/nas/PPython-3.6.1/Lib/hashlib.py", line 243, in <module>
    globals()[__func_name] = __get_hash(__func_name)
  File "/home/nas/PPython-3.6.1/Lib/hashlib.py", line 119, in __get_openssl_constructor
    return __get_builtin_constructor(name)
  File "/home/nas/PPython-3.6.1/Lib/hashlib.py", line 113, in __get_builtin_constructor
    raise ValueError('unsupported hash type ' + name)
ValueError: unsupported hash type blake2s

The issues seems to be resolved. In the future please add the expert for a topic or maintainer of a module to the nosy list of the ticket.

Neil, can this issue be closed or do you want to backport to 3.6?

It should be backported in my opinion.

Create PR 2042 for backport to 3.6 branch.