title: different behavior in Python when creating set from constructor or literal
body: <p>I am trying to create a Set structure in Python by using code below:</p>
  
  <pre><code>a = set ([1,2,3])
  print (a)
  a ={1,2,3}
  print (a)
  a = {'FG'}
  print (a)
  a = set('FG')
  print (a)
  </code></pre>
  
  <p>output:</p>
  
  <pre><code>{1, 2, 3}
  {1, 2, 3}
  {'FG'}
  {'F', 'G'}
  </code></pre>
  
  <p>while the set creation with a list of numbers leads to the same result using the two options,
  I see that if the input type is a String the result that I expect is the second, i.e. create a set of characters, while the first result seems to ignore that a string is a sequence of characters, therefore I am confused.</p>