old_contents: from django import forms
  
  import player
  
  FORM_FIELD_TO_PLAYER_OBJECT = {
      'random_player': player.Player,
      'cooperator': player.Cooperator,
      'betrayer': player.Betrayer,
      'tit_for_tat_player': player.TitForTatPlayer,
  }
  
  
  class TournamentInfoForm(forms.Form):
      random_player = forms.IntegerField()
      cooperator = forms.IntegerField()
      betrayer = forms.IntegerField()
      tit_for_tat_player = forms.IntegerField()
  
new_contents: from django import forms
  
  import player
  
  FORM_FIELD_TO_PLAYER_OBJECT = {
      'random_player': player.Player,
      'cooperator': player.Cooperator,
      'betrayer': player.Betrayer,
      'tit_for_tat_player': player.TitForTatPlayer,
  }
  
  
  class TournamentInfoForm(forms.Form):
      random_player = forms.IntegerField(min_value=0)
      cooperator = forms.IntegerField(min_value=0)
      betrayer = forms.IntegerField(min_value=0)
      tit_for_tat_player = forms.IntegerField(min_value=0)
  
      def clean(self):
          cleaned_data = self.cleaned_data
          if sum(cleaned_data.values()) > 30:
              raise forms.ValidationError(
                  "Too much players, number of total players should less than 30.")
          return cleaned_data
  
subject: add player numbers validation and restriction