use this __init__() for display custom error messages in django forms.py

form custom invalid messages

class MyForm(forms.Form):
    username = forms.CharField(label=_('Your username'), min_length=3, max_length=30)
    email = forms.EmailField(label=_('Your email address'), min_length=3, max_length=30)

    def __init__(self, *args, **kwargs):
        super(MyForm, self).__init__(*args, **kwargs)

        for field in self.fields.values():
            field.error_messages = {
                'required': ugettext('The field : {fieldname} is required !!').format(fieldname=field.label),
                'invalid': ugettext('The field : {fieldname} is invalid !!').format(fieldname=field.label)
            }