django 输入有效日期。验证错误

My model

 class Member(models.Model):

dob = models.DateField('dob')

form

class MemberForm(ModelForm):
  dob = forms.DateField(required=False, input_formats='%Y-%m-%d')
  class Meta:
    model = Member
    exclude = ('profile',)   

一些查看代码

if request.method == 'POST': # If the form has been submitted...
        signup_form = SignupForm(request.POST) # A form bound to the POST data
        # Create a formset from the submitted data
        member_formset = MemberFormSet(request.POST, request.FILES)
        # import pdb; pdb.set_trace()
        if signup_form.is_valid() and member_formset.is_valid():
          print 'in valid'
          signup = signup_form.save(request.POST)
          for form in member_formset.forms:
            member = form.save(commit=False)
            member.profile = signup
            # import pdb; pdb.set_trace()
            # print member.objects.all()
            member.save()
          return redirect("/main") # Redirect to a 'success' page

当我提交表单时出现的错误消息是

Enter a valid date.

我应该做什么来解决这个验证问题。

input_formats需要是一个列表，请参阅

example:

['%Y-%m-%d',      # '2006-10-25'
'%m/%d/%Y',       # '10/25/2006'
'%m/%d/%y']       # '10/25/06'

https://docs.djangoproject.com/en/dev/ref/forms/fields/#django.forms.DateField https://docs.djangoproject.com/en/dev/ref/forms/fields/#django.forms.DateField