title: Running forecast in a loop python (Python newbie trying to learn)
body: <p>I have a dataframe with columns date, sales.
  I ran a ETS model using the code below:</p>
  <pre><code>from statsmodels.tsa.holtwinters import ExponentialSmoothing
  m = ExponentialSmoothing(df.sales,trend='mul',seasonal='mul',seasonal_periods=12).fit()
  forecast=m.forecast(13)
  forecast= pd.DataFrame(m.forecast(13),columns=['sales'])
  </code></pre>
  <p>I am trying to run this on another dataframe with has date, region and sales
  this is what I am trying, please find code below:</p>
  <pre><code>test_df = pd.DataFrame() ## creating empty data frame##
  for region in df: ## trying to iterate over each region##
      test_df['region'] = unique_regions ## trying to add the region value to the empty data drame##
      m = ExponentialSmoothing(df.sales,trend='mul',seasonal='mul',seasonal_periods=12).fit()
      forecast=m.forecast(13)
      forecast= pd.DataFrame(m.forecast(13),columns=['sales'])
      column=df['date']
      max_date=column.max()
      date_list=pd.date_range(start=max_date, periods=14, freq='M')
      date_list=pd.DataFrame(date_list,columns=['date'])
      date_list=date_list.iloc[1:,0]
      date_list=pd.DataFrame(date_list)
      date_list.reset_index()
      date_list.reset_index(inplace=True,drop=True)
      forecast.reset_index(inplace=True,drop=True)
      test_df=forecast.join(date_list,how='outer')
      test_df = test_df[['date','region', 'sales']] ## finally create a df with date,region and the forecasted value##
  test_df
  
  ## append the test_df to df##
  </code></pre>
  <p><strong>Could someone please assist? How do I run the model over each region</strong></p>