Add function for listing duplicates

tcgcore.py

@@ -17,6 +17,15 @@ def ownedcards():
             pass
     return sorted(ownedcards)
 
+def showdupes():
+    dupeslist = []
+    previouscard = ""
+    for card in ownedcards():
+        if card == previouscard:
+            dupeslist.append(card)
+        previouscard = card
+    return dupeslist
+
 def deckcards(deck):
     deckcards = []
     for card in ownedcards():