title: Pandas dataframe value changes from datetime to Timestamp
body: <p>I created a datetime variable and when appended into DataFrame, it automatically converted to Timestamp. how can this happen? anyone can some idea on this?</p>
  
  <pre><code>mydatetime=datetime.datetime(2019,1,22)
  df_test=pd.DataFrame(columns=['datetimecol','value'])
  df_test.loc[len(df_test)]=[mydatetime,12.3]
  df_test
  df_test.datetimecol[0]
  </code></pre>