extend the word-count exercise

python/word-count/word_count.py

@@ -1,7 +1,8 @@
 def count_words(input_sentence):
     sentence = input_sentence.lower()
-    # blocked_characters = [',', '.', ';', ':']
-    # sentence = ''.join(item for item in sentence if item.isalnum())
+    blocked_characters = [',', '.', ';', ':', '_']
+    for character in blocked_characters:
+        sentence = sentence.replace(character, " ")
 
     words = sentence.split()
     result = {}