title: django forms: change attribute of formfield dynamically
body: <p>I have a form like the one below:</p>
  
  <pre><code>class ConsentFormTpl(forms.Form):
      title =  forms.CharField()
      message = forms.CharField(widget=EditorWidget,label='Description')
      acknowledge = forms.BooleanField(label="Require acknowledgement?")
      deadline = forms.DateField(widget=CalendarTimeWidget,label="Acknowledge By")
      start_time = forms.DateTimeField(widget=CalendarTimeWidget)
      end_time = forms.DateTimeField(widget=CalendarTimeWidget)
      availClass  = forms.ModelChoiceField(queryset=SchoolClass.objects.all(),empty_label="Select a class",label='Class')
      consent = forms.BooleanField()
      students = forms.ModelMultipleChoiceField(label="",\
          queryset=User.objects.filter(groups__name='Students').extra(select={'user_name':"first_name || ' ' || last_name"}), \
          widget=FilteredSelectMultiple("Students",is_stacked=False))
      where =  forms.CharField()
      form_name = forms.CharField(label='Save as:')
  
  
      def __init__(self,data=None,draft=False):
          super(ConsentFormTpl,self).__init__(data)
          self.draft = draft
  
          self.acknowledge.required = False
          self.deadline.required = False
          self.start_time.required = False
          self.end_time.required = False
          self.availClass.required = False
          self.consent.required = False
          self.where.required = False
  
          if draft:
              self.title.required = False
              self.message.required = False
              self.students.required = False
              self.form_name.required = True
          else:
              self.form_name.required = False
  </code></pre>
  
  <p>Depending on the value of draft, I want to change the attributes (required) of some of the fields, which was what was in the init method.</p>
  
  <p>However I encountered the following message:</p>
  
  <pre><code>'ConsentFormTpl' object has no attribute 'acknowledge'
  </code></pre>
  
  <p>Anyone knows why?</p>