Tools: Add a script for finding common tags of music files

I want to know the bare minimum of what tags can be relied on in my
music, so this script can help me set default / fallback tags.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

tools/common_tags.py

@@ -0,0 +1,47 @@
+#!/usr/bin/python
+# Copyright 2020 (c) Anna Schumaker
+#
+# Use Mutagen to generate a list of common tag names for
+# all music files in the requested directory
+import mutagen
+import os
+import pathlib
+import sys
+
+if len(sys.argv) != 2 or not os.path.isdir(sys.argv[1]):
+    print(f"Usage: {sys.argv[0]} DIRECTORY")
+    sys.exit(1)
+
+print()
+print(f"Reading directory {sys.argv[1]}:")
+
+files  = [ ]
+for entry in pathlib.Path(sys.argv[1]).rglob("*"):
+    if os.path.isfile(entry):
+        files += [ entry ]
+
+print(f"  Found {len(files)} files")
+
+read = 0
+skip = 0
+unique = None
+for f in files:
+    try:
+        keys = set(mutagen.File(f).keys())
+        if unique == None:
+            unique = keys
+        else:
+            unique = unique.intersection(keys)
+        read += 1
+    except Exception as e:
+        #print(e)
+        skip += 1
+
+print(f"  Read {read} files, skipped {skip}")
+
+tags = list(unique)
+tags.sort()
+print(f"  There are {len(tags)} common tags:")
+for t in tags:
+    print(f"    {t}")
+print()