switch to importlib.metadata for entrypoint loading

Importing pkg_resources scans every installed distribution to find
all of the entry points. importlib.metadata can import entry points
without scanning all of the installed packages.

Change-Id: I9917b10292d191710b37838b3cf099d75139f123
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

lower-constraints.txt

@@ -6,6 +6,7 @@ decorator==4.4.1
 doc8==0.8.0
 dogpile.cache==0.6.5
 fixtures==3.0.0
+importlib_metadata==1.7.0
 iso8601==0.1.11
 jmespath==0.9.0
 jsonpatch==1.16

openstack/connection.py

@@ -179,6 +179,13 @@ Additional information about the services can be found in the
 import warnings
 import weakref
 
+try:
+    # For python 3.8 and later
+    import importlib.metadata as importlib_metadata
+except ImportError:
+    # For everyone else
+    import importlib_metadata
+
 import concurrent.futures
 import keystoneauth1.exceptions
 import requestsexceptions
@@ -423,15 +430,17 @@ class Connection(
                     (package_name, function) = vendor_hook.rsplit(':')
 
                     if package_name and function:
-                        import pkg_resources
-                        ep = pkg_resources.EntryPoint(
-                            'vendor_hook', package_name, attrs=(function,))
-                        hook = ep.resolve()
+                        ep = importlib_metadata.EntryPoint(
+                            name='vendor_hook',
+                            value=vendor_hook,
+                            group='vendor_hook',
+                        )
+                        hook = ep.load()
                         hook(self)
                 except ValueError:
                     self.log.warning('Hook should be in the entrypoint '
                                      'module:attribute format')
-            except (ImportError, TypeError) as e:
+            except (ImportError, TypeError, AttributeError) as e:
                 self.log.warning('Configured hook %s cannot be executed: %s',
                                  vendor_hook, e)
 

requirements.txt

@@ -17,3 +17,5 @@ netifaces>=0.10.4 # MIT
 
 dogpile.cache>=0.6.5 # BSD
 cryptography>=2.1 # BSD/Apache-2.0
+
+importlib_metadata>=1.7.0;python_version<'3.8' # Apache-2.0