Newsletter signup form

forms.py

class NewsLetterSignupForm(forms.ModelForm):
    class Meta:
        model = NewsLetterSignup
        fields = ['email']
    
    def save(self, commit=True):
        """Return an existing instance if one exists with the same email.
        Create and return it otherwise.
        
        """
        email = self.cleaned_data['email']
        # XXX: This is not atomic and is suceptible to race conditions where two
        # models with the same email address could be created.
        try:
            return NewsLetterSignup.objects.get(email=email)
        except NewsLetterSignup.DoesNotExist:
            return super(NewsLetterSignupForm, self).save(commit)