diff --git a/source/Collection_Data_Types.rst b/source/Collection_Data_Types.rst
index 40de3b790230eb9d4572514b163f365c54a79d0f..f21d84cd87f07849613dfeea8aee4ea6f5863607 100644
--- a/source/Collection_Data_Types.rst
+++ b/source/Collection_Data_Types.rst
@@ -275,6 +275,16 @@ solution ::
    for kmer, occurence in kmers.items():
       print kmer, " = ", occurence
 
+we can use also a defaultdict: ::
+
+   import collections
+   
+   s = s.replace('\n', '')
+   kmers = collection.defaultdict(int)
+   for i in range(len(s) - 3):
+      kmer = s[i:i+3]
+      kmers[kmer] += 1
+
 solution bonus ::
 
    list_of_kmers = kmers.items()