called with an argument string 'Unknown', tuple with 2 elements: string '2' and return value of the function ugettext_lazy, called with an argument string 'Yes' and tuple with 2 elements: string '3' and return value of the function ugettext_lazy, called with an argument string 'No'. call the method __init__ from the base class of the class NullBooleanSelect, with arguments attrs and choices.
super ( NullBooleanSelect , self ) . __init__ ( attrs , choices )