Refactor characters which should not be bothered into a whitelist

normalisename.py

@@ -3,16 +3,18 @@ from os import rename
 from unidecode import unidecode
 
 
+# whitespaces will be replaced
+# dots are ok
+# do not ruin previous work
+# dashes are ok
+whitelist = [' ', '.', '_', '-']
+
 for file in argv[1:]:
     rename(file,
            unidecode
            (
                ''.join(ch for ch in file
                        if ch.isalnum()
-                       or ch is ' '     # whitespaces will be replaced
-                       or ch is '.'     # dots are ok
-                       or ch is '_'     # do not ruin previous work
-                       or ch is '-')    # dashes are ok
+                       or ch in whitelist)
            )
            .replace(' ', '_'))
-