title: In pandas how to use drop_duplicates with one exception?
body: <p>In python 3 and pandas I need to eliminate duplicate rows from a dataframe by repeating values in a column. For this I used:</p>
  
  <pre><code>consolidado = df_processos.drop_duplicates(['numero_unico'], keep='last')
  </code></pre>
  
  <p>The column "numero_unico" has codes in string format like 0029126-45.2019.1.00.0000, 0026497-98.2019.1.00.0000, 0027274-83.2019.1.00.0000...</p>
  
  <p>So the above command keeps only the last string code appearance found</p>
  
  <p>Please does anyone know how to use drop_duplicates with one exception?</p>
  
  <p>But the column contents will not always be string codes. In several lines appears the content "Sem número único"</p>
  
  <p>And I want to keep all the lines where this exception exists. But with the above command the generated dataframe keeps only the last appearance of "Sem número único"</p>