title: python - how to use the join method and sort method
body: <p>My purpose is to get an input as a string and return a list of lower case letters of that string, without repeats, without punctuations, in alphabetical order. For example, the input &quot;happy!&quot; would get ['a','h','p','y']. I try to use the join function to get rid of my punctuations but somehow it doesn't work. Does anybody know why? Also, can sort.() sort alphabets? Am I using it in the right way? Thanks!</p>
  <pre><code>def split(a):
      a.lower()
      return [char for char in a]
  
  def f(a):
      i=split(a)
      s=set(i)
      l=list(s)
      v=l.join(u for u in l if u not in (&quot;?&quot;, &quot;.&quot;, &quot;;&quot;, &quot;:&quot;, &quot;!&quot;))
      v.sort()
      return v
  </code></pre>