[3.6] replace dynamic import with 'exec' with importlib.import_module (GH-5433) (GH-5440)

(cherry picked from commit 77526f05)

Lib/test/test_hashlib.py

@@ -9,6 +9,7 @@
 import array
 from binascii import unhexlify
 import hashlib
+import importlib
 import itertools
 import os
 import sys
@@ -86,11 +87,11 @@ class HashLibTestCase(unittest.TestCase):
     def _conditional_import_module(self, module_name):
         """Import a module and return a reference to it or None on failure."""
         try:
-            exec('import '+module_name)
-        except ImportError as error:
+            return importlib.import_module(module_name)
+        except ModuleNotFoundError as error:
             if self._warn_on_extension_import:
                 warnings.warn('Did a C extension fail to compile? %s' % error)
-        return locals().get(module_name)
+        return None
 
     def __init__(self, *args, **kwargs):
         algorithms = set()