use importlib.metadata to get keyring version

Importing pkg_resources has a side-effect of scanning the metadata of
all of the installed python modules to build an in-memory cache. That
cache isn't used anywhere in keystoneclient, and it can be expensive
to build.

The importlib.metadata module in the 3.8 standard library (and the
importlib_metadata library for earlier versions) provides the same
version lookup service using a more efficient scanning
implementation. Switching from pkg_resources to importlib.metadata
will help application startup time, which is especially important for
command line programs such as python-openstackclient.

Change-Id: Ia89044ff1876eeb2793cd08ed9095ce2ffe89e09
Depends-On: Ic6db7af34c87a636bfe55bacae03c42154f4b9c7
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

1 files changed, 13 insertions, 5 deletions

diff --git a/keystoneclient/httpclient.py b/keystoneclient/httpclient.py
index 8d157ce..83684e2 100644
--- a/keystoneclient/httpclient.py
+++ b/keystoneclient/httpclient.py
@@ -20,11 +20,18 @@
 import logging
 import warnings
 
+try:
+    # For Python 3.8 and later
+    import importlib.metadata as importlib_metadata
+except ImportError:
+    # For everyone else
+    import importlib_metadata
+
 from debtcollector import removals
 from debtcollector import renames
 from keystoneauth1 import adapter
 from oslo_serialization import jsonutils
-import pkg_resources
+import packaging.version
 import requests
 
 try:
@@ -33,9 +40,10 @@ try:
     # NOTE(sdague): The conditional keyring import needs to only
     # trigger if it's a version of keyring that's supported in global
     # requirements. Update _min and _bad when that changes.
-    keyring_v = pkg_resources.parse_version(
-        pkg_resources.get_distribution("keyring").version)
-    keyring_min = pkg_resources.parse_version('5.5.1')
+    keyring_v = packaging.version.Version(
+        importlib_metadata.version('keyring')
+    )
+    keyring_min = packaging.version.Version('5.5.1')
     # This is a list of versions, e.g., pkg_resources.parse_version('3.3')
     keyring_bad = []
 
@@ -43,7 +51,7 @@ try:
         import keyring
     else:
         keyring = None
-except (ImportError, pkg_resources.DistributionNotFound):
+except (ImportError, importlib_metadata.PackageNotFoundError):
     keyring = None
     pickle = None