Remove python 3.7 and 3.8 support

Conda install of cvxpy automatically installs python 3.9, so there's no point in trying to support earlier python versions.

.github/workflows/python-build.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ['3.7', '3.8', '3.9']
+        python-version: ['3.9']
 
     steps:
     - uses: actions/checkout@v2

qf_diamond_norm/config.py

@@ -11,14 +11,7 @@
 import re
 import sys
 import typing
-
-try:
-    # python >= 3.8
-    from importlib import metadata as importlib_metadata  # type: ignore
-except ImportError:  # pragma: no cover
-    # python == 3.7
-    import importlib_metadata  # type: ignore  # noqa: F401
-
+from importlib import metadata as importlib_metadata  # type: ignore
 
 __all__ = ["__version__", "about"]
 

setup.cfg

@@ -23,8 +23,6 @@ Classifiers=
     Natural Language :: English
     Operating System :: OS Independent    
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.7
-    Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
     Topic :: Scientific/Engineering    
     Topic :: Software Development :: Libraries
@@ -33,11 +31,9 @@ Classifiers=
 
 [options]
 zip_safe = True
-python_requires = >= 3.7
+python_requires = >= 3.9
 
-# importlib_metadata required for python 3.7
 install_requires =
-    importlib_metadata
     quantumflow
     cvxpy