title: why 'in' operator with tuple as a key in python so slow?
body: <p>I have a dict such as:</p>
  
  <pre><code>d=dict()
  d[('1','2')] = 'value'
  </code></pre>
  
  <p>Then I query the key :</p>
  
  <pre><code>if (k1,k2) in d.keys():
  </code></pre>
  
  <p>When there is million records,the speed is a suffering, any problem with the 'in' operator?</p>
  
  <p>Is it sequential search?</p>
  
  <p>I have to  concat str as key to bypass this issue.</p>