Identify the nature of field error in django forms - django-templates

Question

The 2 types of validation error a form field in django can have are 'required' and 'invalid'. Is there any way to find out which of these two errors has happened, from the template? Something like
{% if form.username.errors %}
{% for error in form.username.errors %}
{% if error.required %}
Please enter the username
{% else %}
{{ error }}
{% endif %}
I just want to override the error message for the 'required' error, i.e., I want to display my own error message if that error happens. I am using django.contrib.auth.views which uses django.contrib.auth.forms.AuthenticationForm which I don't want to try customizing.

Answer 1

Hope you are searching for this type of handle in html template
{% for x in form.errors %}
{%if "__all__" in x %}
Wrong username and password
{%else%}
{%if "username" in x %}
Requires username
<br>
{%endif%}
{%if "password" in x %}
Requires Password
<br>
{%endif%}
{%endif%}
{%endfor%}
Messages will be printed like this on your login page
Requires username
Requires Password
Wrong username and password

Answer 2

You really should just override the Authentication form. The view accepts an argument that allows for you to override form easily.
I think something like this should work:
All you need to do is override the clean_username method like so:
edit:
overriding the clean_username method fails to change the validation error message because of the following from the form and field validation docs:
The clean() method on a Field
subclass. This is responsible for
running to_python, validate and
run_validators in the correct order
and propagating their errors. If, at
any time, any of the methods raise
ValidationError, the validation stops
and that error is raised. This method
returns the clean data, which is then
inserted into the cleaned_data
dictionary of the form.
The clean_<fieldname>() method in a
form subclass – where is
replaced with the name of the form
field attribute. This method does any
cleaning that is specific to that
particular attribute, unrelated to the
type of field that it is. This method
is not passed any parameters. You will
need to look up the value of the field
in self.cleaned_data and remember that
it will be a Python object at this
point, not the original string
submitted in the form (it will be in
cleaned_data because the general field
clean() method, above, has already
cleaned the data once).
The Field subclass is validated first and returns the cleaned data that is used for the clean_<field_name>() method. If an error occurs there the validation of that field stops.
This means that to override the message you need to either override the Field validation or make the field not require a value so no validation error is raised at that step and raise a required method in the clean_<fieldname>() method
>>> from django.contrib.auth.forms import AuthenticationForm
>>> class MyAuthForm(AuthenticationForm):
... def __init__(self, *args, **kwargs):
... super(MyAuthForm, self).__init__(*args,**kwargs)
... self.fields['username'].error_messages['required']='Custom Required Msg'
...
>>> form = MyAuthForm(data={'password':'asdf'})
>>> form.is_valid()
False
>>> form.errors
{'username': [u'Custom Required Msg']}
>>>
urls.py
from someapp.forms import MyAuthForm
urlpatterns = patterns('',
...
(r'^accounts/login/$', 'django.contrib.auth.views.login', {'template_name': 'someapp/login.html', 'authentication_form':MyAuthForm, }),
...