title: Can not merge df2 to df1 despite shared values in Python Pandas?
body: <p>I have really strange situation. I try to merge two DataFrames using one common column like below:</p>
  <pre><code>df1.merge(df2, on = &quot;customer_id&quot;, how = &quot;left&quot;) 
  </code></pre>
  <p>Nevertheless, no columns from df2 join df1 even though they share customer_id. In both DataFrames customer_id is same type &quot;int&quot;. How it is possible? What can I do ?</p>