title: Check if list of keys exist in dictionary
body: <p>I have a dictionary that looks like that:</p>
  
  <pre><code>grades = {
          'alex' : 11,
          'bob'  : 10,
          'john' : 14,
          'peter': 7
         }
  </code></pre>
  
  <p>and a list of names <code>students = ('alex', 'john')</code></p>
  
  <p>I need to check that all the names in <code>students</code> exist as keys in <code>grades</code> dict.</p>
  
  <p><code>grades</code> can have more names, but all the names in <code>students</code> should be in <code>grades</code></p>
  
  <p>There must be a straightforward way to do it, but i'm still new to python and can't figure it out. tried <code>if students in grades</code>, didn't work.</p>
  
  <p>In the actual cases, the lists will be much bigger.</p>