switch to importlib.metadata to find package version

Importing pkg_resources has a side-effect of reading all of the
metadata for every installed python package. The newer
importlib.metadata module can load the metadata for one package at a
time, which makes this library load more quickly and improves the
startup-time performance of applications that use it such as
python-openstackclient.

importlib.metadata is part of the python 3.8 standard library and is
distributed separately for other versions of python.

Change-Id: Ib1870a3d102116f84c7677601fd44fdac41a13a6
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

lower-constraints.txt

@@ -2,6 +2,7 @@ coverage===4.0
 ddt===1.0.1
 dulwich===0.15.0
 elasticsearch===2.0.0
+importlib_metadata==1.7.0
 jaeger-client==3.8.0
 netaddr===0.7.18
 openstackdocstheme==2.2.1

osprofiler/__init__.py

@@ -13,6 +13,11 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import pkg_resources
+try:
+    # For Python 3.8 and later
+    import importlib.metadata as importlib_metadata
+except ImportError:
+    # For everyone else
+    import importlib_metadata
 
-__version__ = pkg_resources.get_distribution("osprofiler").version
+__version__ = importlib_metadata.version("osprofiler")

requirements.txt

@@ -6,3 +6,4 @@ PrettyTable<0.8,>=0.7.2 # BSD
 requests>=2.14.2 # Apache-2.0
 six>=1.10.0 # MIT
 WebOb>=1.7.1 # MIT
+importlib_metadata>=1.7.0;python_version<'3.8' # Apache-2.0