count: added v3 and v4 after reading about Trey's solution.

count/count.py

@@ -1,5 +1,5 @@
 import re
-from collections import defaultdict
+from collections import defaultdict, Counter
 
 
 def count_words_v1(sentence):
@@ -17,4 +17,18 @@ def count_words_v2(sentence):
     return count
 
 
-count_words = count_words_v2
+def count_words_v3(sentence):
+    """Augmented by trey's regex."""
+    regex = r"\b[\w'-]+\b"
+    count = defaultdict(int)
+    for word in re.findall(regex, sentence):
+        count[word.lower()] += 1
+    return count
+
+
+def count_words_v4(sentence):
+    """And the most compact yet pythonic solution."""
+    return Counter(re.findall(r"\b[\w'-]+\b", sentence.lower()))
+
+
+count_words = count_words_v4