save keys to exclude as a global variable

Author: yucongalicechen

src/diffpy/labpdfproc/tools.py

@@ -4,6 +4,7 @@
 
 WAVELENGTHS = {"Mo": 0.71, "Ag": 0.59, "Cu": 1.54}
 known_sources = [key for key in WAVELENGTHS.keys()]
+METADATA_KEYS_TO_EXCLUDE = ["output_correction", "force_overwrite", "input", "input_paths"]
 
 
 def set_output_directory(args):
@@ -240,8 +241,7 @@ def load_metadata(args, filepath):
 
     args = _set_anode_type(args)
     metadata = vars(args)
-    exclude_keys = ["output_correction", "force_overwrite", "input", "input_paths"]
-    for key in exclude_keys:
+    for key in METADATA_KEYS_TO_EXCLUDE:
         metadata.pop(key, None)
     metadata["input_directory"] = str(filepath)
     metadata["output_directory"] = str(metadata["output_directory"])