title: ValueError while doing merge with DataFrames using Pandas
body: <p>I am trying to merge three DataFrames using Pandas. Why do I get this error message?</p>
  <blockquote>
  <p>ValueError: The truth value of a DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().</p>
  </blockquote>
  <p>This is the code:</p>
  <pre><code>df=pd.merge(energy,GDP,ScimEn,on=&quot;Country&quot;)
  </code></pre>
  <p>Here <code>energy</code>,<code>GDP</code>,<code>ScimEn</code> are the three DataFrames I was trying to merge.</p>