How can I extract list items using dictionary keys?
<p>I have list and dictionary like this:</p>

<pre><code>list_1 = ['if looks kill then i'm murdering]

dic_1 = {"kill": -2, "murdering": -3}
</code></pre>

<p>I want to extract list items that matches the dictionary key and append it to a set. 
I have two problems:
1. I cannot extract the list items that matches with key in the dictionary
2. How do I append list items to a set?</p>

<pre><code>set_1 = set()
for items in list_1:
   list_1 = items.lower().split()

   for term in dic_1:

      forth_list = [words for words in list_1 if term != words]
      print forth_list
</code></pre>

<h1>This will print</h1>

<pre><code>['if', 'looks', 'then', 'i', 'm', 'murdering']
['if', 'looks', 'kill', 'then', 'i', 'm']

set_1.add(forth_list) # this produce a TypeError: unhashable type: 'list'
print set_1      
</code></pre>
