Better explain that items need to be hashable.

Eric Naeseth · Eric Naeseth · commit d37e7e11c03a · 2009-03-10T16:37:13.000-05:00
diff --git a/Readme.md b/Readme.md
@@ -27,7 +27,8 @@ in your transactions with the following code:
         print itemset
         
 Note that `find_frequent_itemsets` returns a generator of itemsets, not a
-greedily-populated list.
+greedily-populated list. Each item must be hashable (i.e., it must be valid as
+a member of a dictionary or a set).
 
 Script Usage
 ------------
diff --git a/fp_growth.py b/fp_growth.py
@@ -24,6 +24,9 @@ def find_frequent_itemsets(transactions, minimum_support):
     The `transactions` parameter can be any iterable of iterables of items.
     `minimum_support` should be an integer specifying the minimum number of
     occurrences of an itemset for it to be accepted.
+    
+    Each item must be hashable (i.e., it must be valid as a member of a
+    dictionary or a set).
     """
     items = defaultdict(lambda: 0) # mapping from items to their supports
     processed_transactions = []
