MNT: Move to exec_module instead of load_module (#1369)

* move to exec_module instead of load_module

* add check for colormap in config

pyart/config.py

@@ -59,9 +59,14 @@ def load_config(filename=None):
     global _DEFAULT_FIELD_LIMITS
 
     try:
-        from importlib.machinery import SourceFileLoader
+        from importlib.util import module_from_spec, spec_from_file_location
+
+        spec = spec_from_file_location("metadata_config", filename)
+        # assert spec is not None
+        cfile = module_from_spec(spec)
+        # assert spec.loader is not None
+        spec.loader.exec_module(cfile)
 
-        cfile = SourceFileLoader("metadata_config", filename).load_module()
     except ImportError:
         import imp
 
@@ -72,8 +77,13 @@ def load_config(filename=None):
     _FIELD_MAPPINGS = cfile.FIELD_MAPPINGS
     _FILL_VALUE = cfile.FILL_VALUE
     _DEFAULT_FIELD_NAMES = cfile.DEFAULT_FIELD_NAMES
-    _DEFAULT_FIELD_COLORMAP = cfile.DEFAULT_FIELD_COLORMAP
-    _DEFAULT_FIELD_LIMITS = cfile.DEFAULT_FIELD_LIMITS
+
+    # These last two are optional
+    try:
+        _DEFAULT_FIELD_COLORMAP = cfile.DEFAULT_FIELD_COLORMAP
+        _DEFAULT_FIELD_LIMITS = cfile.DEFAULT_FIELD_LIMITS
+    except:
+        pass
     return