title: Number of elements in Python Set
body: <p>I have a list of phone numbers that have been dialed (nums_dialed).
  I also have a set of phone numbers which are the number in a client's office (client_nums)
  How do I efficiently figure out how many times I've called a particular client (total)</p>
  
  <p>For example:</p>
  
  <pre><code>&gt;&gt;&gt;nums_dialed=[1,2,2,3,3]
  &gt;&gt;&gt;client_nums=set([2,3])
  &gt;&gt;&gt;???
  total=4
  </code></pre>
  
  <p>Problem is that I have a large-ish dataset: len(client_nums) ~ 10^5; and len(nums_dialed) ~10^3.</p>