Or, use a defaultdict(int), or more in line with yours: d[word] = d.get(word,0) + 1 dictionary.get is quite useful. Also, I'd consider s.split(None), instead

Or, use a defaultdict(int), or more in line with yours: d[word] = d.get(word,0) + 1 dictionary.get is quite useful. Also, I'd consider s.split(None), instead of s.split(' '). It will group whitespace, so that any double space or other whitespace is collapsed into one delimiter.