How to update User object without creating new one? - django

Question

Following works fine in shell:
>>> from django.contrib.auth.models import User
>>> user=User.objects.get(pk=1)
>>> user.first_name = u'Some'
>>> user.last_name = u'Name'
>>> user.save()
>>> user.first_name
u'Some'
>>> user.last_name
u'Name'
Then I try to do the same with forms:
# forms.py
class UserForm(forms.ModelForm):
class Meta:
model = User
fields = ['first_name', 'last_name']
# views.py
def edit_names(request, template_name="registration/edit_names.html"):
if request.method == "POST":
form = UserForm(data=request.POST)
if form.is_valid():
user = form.save(commit=False)
user.save()
url = urlresolvers.reverse('my_account')
return HttpResponseRedirect(url)
else:
form = UserForm(instance=request.user)
page_title = _('Edit user names')
return render_to_response(template_name, locals(),
context_instance=RequestContext(request))
# edit_names.html
<form action="." method="post">{% csrf_token %}
<table>
{{ form.as_table }}
<tr><td colspan="2">
<input type="submit" />
</td></tr>
</table>
</form>
I open page in browser and see two fields First name and Last name. When I fill in the fields and submit the form I get the error:
Exception Type: IntegrityError
Exception Value: column username is not unique
I also tried to add ['username'] to fields list in UserForm. If I submit the form with my username (as request.user), the form displays errormessage:
User with this Username already exists.
If I change the username to some unique name, the new user with that username is being created.
The question is:
How can I update User object, not create new one?
Sorry for being so verbose, but I had hard search here and could not find the answer to my question.
BTW, these cases don't work for me:
Extending UserCreationForm to include email, first name, and last name
add field first_name and last_name in django-profile
How to create a UserProfile form in Django with first_name, last_name modifications?
EDIT:
As suggested #fceruti I just added on request.method == 'post' branch this:
form = UserForm(data=request.POST, instance=request.user)

Answer 1

Just add on request.method == 'post' branch this:
form = UserForm(data=request.POST, instance=request.user)

Answer 2

if request.method == "POST":
kwargs = { 'data' : request.POST }
try:
kwargs['instance'] = User.objects.get(username=request.POST['username'])
except:
pass
form = UserForm(kwargs**)
if form.is_valid():
user = form.save(commit=False)
...