[Python] Replace pkg_resources

The import time for pkg_resources is significant. As of Python 3.8, the
two commands we use can be replace by 'importlib.metadata.version' and the
lighter-weight 'packaging.version.parse'.

SConstruct

@@ -78,7 +78,10 @@ import subprocess
 import re
 import json
 import textwrap
-from pkg_resources import parse_version
+try:
+    from packaging.version import parse as parse_version
+except ImportError:
+    from pkg_resources import parse_version
 import SCons
 
 # ensure that Python and SCons versions are sufficient for the build process

interfaces/cython/cantera/_utils.pyx

@@ -6,13 +6,13 @@ import os
 import warnings
 from cpython.ref cimport PyObject
 import numbers
-import pkg_resources
+import importlib.metadata
 import numpy as np
 
 # avoid explicit dependence of cantera on scipy
 try:
-    pkg_resources.get_distribution('scipy')
-except pkg_resources.DistributionNotFound:
+    importlib.metadata.version('scipy')
+except importlib.metadata.PackageNotFoundError:
     _scipy_sparse = ImportError('Method requires a working scipy installation.')
 else:
     from scipy import sparse as _scipy_sparse
@@ -103,8 +103,8 @@ def hdf_support():
     """
     out = []
     try:
-        pkg_resources.get_distribution("h5py")
-    except pkg_resources.DistributionNotFound:
+        importlib.metadata.version("h5py")
+    except importlib.metadata.PackageNotFoundError:
         pass
     else:
         out.append("h5py")

interfaces/cython/cantera/composite.py

@@ -6,24 +6,22 @@ from ._cantera import *
 import numpy as np
 from collections import OrderedDict
 import csv as _csv
+import importlib.metadata
 
 def _import_h5py():
     # avoid explicit dependence of cantera on h5py
-    import pkg_resources  # local import to reduce overall import time
     try:
-        pkg_resources.get_distribution('h5py')
-    except pkg_resources.DistributionNotFound:
+        importlib.metadata.version('h5py')
+    except importlib.metadata.PackageNotFoundError:
         raise ImportError('Method requires a working h5py installation.')
     else:
         import h5py
         return h5py
 
 # avoid explicit dependence of cantera on pandas
-import pkg_resources
-
 try:
-    pkg_resources.get_distribution('pandas')
-except pkg_resources.DistributionNotFound:
+    importlib.metadata.version('pandas')
+except importlib.metadata.PackageNotFoundError:
     _pandas = ImportError('Method requires a working pandas installation.')
 else:
     import pandas as _pandas

interfaces/cython/setup.cfg.in

@@ -42,6 +42,7 @@ include_package_data = True
 install_requires =
     numpy >= 1.12.0
     ruamel.yaml >= 0.15.34
+    packaging
 python_requires = >=@py_min_ver_str@
 packages =
     cantera

interfaces/python_sdist/setup.cfg.in

@@ -42,6 +42,7 @@ include_package_data = True
 install_requires =
     numpy >= 1.12.0
     ruamel.yaml >= 0.15.34
+    packaging
 python_requires = >=@py_min_ver_str@
 packages =
     cantera

site_scons/buildutils.py

@@ -11,7 +11,10 @@ import time
 import shutil
 import enum
 from pathlib import Path
-from pkg_resources import parse_version
+try:
+    from packaging.version import parse as parse_version
+except ImportError:
+    from pkg_resources import parse_version
 import logging
 from typing import TYPE_CHECKING
 from collections.abc import Mapping as MappingABC
@@ -1352,7 +1355,10 @@ def get_pip_install_location(
     root = quoted(root) if root is not None else None
     install_script = textwrap.dedent(f"""
         from pip import __version__ as pip_version
-        from pkg_resources import parse_version
+        try:
+            from packaging.version import parse as parse_version
+        except ImportError:
+            from pkg_resources import parse_version
         import pip
         import json
         pip_version = parse_version(pip_version)

test/python/test_kinetics.py

@@ -1,7 +1,7 @@
 import numpy as np
 import re
 import itertools
-import pkg_resources
+import importlib.metadata
 import pytest
 
 import cantera as ct
@@ -10,8 +10,8 @@ from .utilities import allow_deprecated
 
 # avoid explicit dependence of cantera on scipy
 try:
-    pkg_resources.get_distribution('scipy')
-except pkg_resources.DistributionNotFound:
+    importlib.metadata.version('scipy')
+except importlib.metadata.PackageNotFoundError:
     _scipy_sparse = ImportError('Method requires a working scipy installation.')
 else:
     from scipy import sparse as _scipy_sparse