swh.model.hashutil: Make unknown variable length algo creation break

Remove the limit on the python3 version, this should be transparent.
If the hash requested is not available, this will raise with an
explanation on the error.

Related T692

swh/model/hashutil.py

@@ -7,7 +7,6 @@ import binascii
 import functools
 import hashlib
 import os
-import sys
 
 from io import BytesIO
 
@@ -77,16 +76,11 @@ def _new_hash(algo, length=None):
             raise ValueError('Missing length for git hashing algorithm')
         base_algo = algo[:-4]
         h = _new_git_hash(base_algo, 'blob', length)
-    elif ':' in algo:   # variable length hashing algorithms (only from
-                        # python3 >= 3.6)
-        if sys.version_info.major == 3 and sys.version_info.minor >= 6:
-            _algo = algo.split(':')
-            base_algo = _algo[0]
-            variable_length = int(_algo[1])
-
-            h = hashlib.new('%s%s' % (base_algo, variable_length))
-        else:
-            raise ValueError('Unsupported hashing algorithm %s' % algo)
+    elif ':' in algo:   # variable length hashing algorithms
+        _algo = algo.split(':')
+        base_algo = _algo[0]
+        variable_length = int(_algo[1])
+        h = hashlib.new('%s%s' % (base_algo, variable_length))
     else:
         h = hashlib.new(algo)
 

swh/model/tests/test_hashutil.py

@@ -8,7 +8,7 @@ import tempfile
 import unittest
 
 from nose.tools import istest
-from unittest.mock import MagicMock, patch
+from unittest.mock import patch
 
 from swh.model import hashutil
 
@@ -131,24 +131,11 @@ class Hashutil(unittest.TestCase):
             hashutil._new_hash('blake2:10')
         except ValueError as e:
             self.assertEquals(str(e),
-                              'Unsupported hashing algorithm blake2:10')
+                              'unsupported hash type blake210')
 
-    @patch('swh.model.hashutil.sys')
-    @istest
-    def new_hash_unexpected_hashing_algo(self, mock_sys):
-        mock_sys.version_info = MagicMock(major=3, minor=6)
-
-        try:
-            hashutil._new_hash('blake3:256')
-        except ValueError as e:
-            self.assertEquals(str(e),
-                              'unsupported hash type blake3256')
-
-    @patch('swh.model.hashutil.sys')
     @patch('swh.model.hashutil.hashlib')
     @istest
-    def new_hash_blake2b(self, mock_hashlib, mock_sys):
-        mock_sys.version_info = MagicMock(major=3, minor=6)
+    def new_hash_blake2b(self, mock_hashlib):
         mock_hashlib.new.return_value = 'some-hashlib-object'
 
         h = hashutil._new_hash('blake2b:512')
@@ -156,17 +143,14 @@ class Hashutil(unittest.TestCase):
         self.assertEquals(h, 'some-hashlib-object')
         mock_hashlib.new.assert_called_with('blake2b512')
 
-    @patch('swh.model.hashutil.sys')
     @patch('swh.model.hashutil.hashlib')
     @istest
-    def new_hash_blake2s(self, mock_hashlib, mock_sys):
-        mock_sys.version_info = MagicMock(major=3, minor=6)
+    def new_hash_blake2s(self, mock_hashlib):
         mock_hashlib.new.return_value = 'some-hashlib-object'
 
         h = hashutil._new_hash('blake2s:256')
 
         self.assertEquals(h, 'some-hashlib-object')
-        mock_hashlib.blake2s.assert_called_with(digest_size=128)
         mock_hashlib.new.assert_called_with('blake2s256')