django: source code of usercreate form is awesome

forms.py

class UserCreationForm(forms.ModelForm):
    """
    A form that creates a user, with no privileges, from the given username and password.
    """
    username = forms.RegexField(label=_("Username"), max_length=30, regex=r'^[\w.@+-]+$',
        help_text = _("Required. 30 characters or fewer. Letters, digits and @/./+/-/_ only."),
        error_messages = {'invalid': _("This value may contain only letters, numbers and @/./+/-/_ characters.")})
    password1 = forms.CharField(label=_("Password"), widget=forms.PasswordInput)
    password2 = forms.CharField(label=_("Password confirmation"), widget=forms.PasswordInput,
        help_text = _("Enter the same password as above, for verification."))

    class Meta:
        model = User
        fields = ("username",)

    def clean_username(self):
        username = self.cleaned_data["username"]
        try:
            User.objects.get(username=username)
        except User.DoesNotExist:
            return username
        raise forms.ValidationError(_("A user with that username already exists."))

    def clean_password2(self):
        password1 = self.cleaned_data.get("password1", "")
        password2 = self.cleaned_data["password2"]
        if password1 != password2:
            raise forms.ValidationError(_("The two password fields didn't match."))
        return password2

    def save(self, commit=True):
        user = super(UserCreationForm, self).save(commit=False)
        user.set_password(self.cleaned_data["password1"])
        if commit:
            user.save()
        return user

真心很头痛,最怕这种逻辑了...