title: Concatenate dataframes in a for loop
body: <p>I wrote a class to scrape public holiday data, but i would like to iterate my class with many years like : </p>
  
  <pre><code>outputt_path = "C:/Users/N000193384/Downloads/countries/"
  recent_years = ["2015", "2016", "2017", "2018"]
  for year in recent_years : 
      PBC = Event_Scraper("italy", year, outputt_path)
      df = PBC._read_html_()
      df = df.append(df)
  </code></pre>
  
  <p>my class took the country's name and the year, outputt_path is useless there. </p>
  
  <p>_read_html_() builds a cleaned dataframe 
  and i would like to append each dataframe.</p>
  
  <p>Here is an example of the dataframe for one year :</p>
  
  <pre><code>    Date    Holiday Name    Holiday Type
  0   2018-01-01  New Year's Day  National holiday
  1   2018-01-06  Epiphany    National holiday
  2   2018-03-20  March Equinox   Season
  3   2018-03-30  Good Friday Observance
  4   2018-04-01  Easter Day  National holiday
  </code></pre>