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>

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
 

lower-constraints.txt

@@ -16,6 +16,7 @@ future==0.16.0
 gitdb==0.6.4
 GitPython==1.0.1
 idna==2.6
+importlib_metadata==1.7.0
 iso8601==0.1.11
 jsonschema==2.6.0
 keyring==5.5.1
@@ -40,6 +41,7 @@ oslo.log==3.36.0
 oslo.serialization==2.18.0
 oslo.utils==3.33.0
 oslotest==3.2.0
+packaging==20.4
 paramiko==2.0.0
 pbr==2.0.0
 pep257==0.7.0

requirements.txt

@@ -13,3 +13,5 @@ oslo.utils>=3.33.0 # Apache-2.0
 requests>=2.14.2 # Apache-2.0
 six>=1.10.0 # MIT
 stevedore>=1.20.0 # Apache-2.0
+importlib_metadata>=1.7.0;python_version<'3.8' # Apache-2.0
+packaging>=20.4 # BSD