Analysis of the common operations of cookies and sessions in Django project development

.has_key('<cookie_name>')

('visits', '1')
if 'last_visit' in :
 ['last_visit']

response.set_cookie('<cookie_name>', value)

fav_color = ('fav_color', 'red')
fav_color = ['fav_color']

['visits'] = visits

del ['fav_color']

'fav_color' in 

python  clearsessions

#Register
def regist(req):
  if  == 'POST':
    uf = UserForm()
    if uf.is_valid():
      # Get form data
      username = uf.cleaned_data['username']
      password = uf.cleaned_data['password']
      # Add to database
      (username= username,password=password)
      return HttpResponse('regist success!!')
  else:
    uf = UserForm()
  return render_to_response('',{'uf':uf}, context_instance=RequestContext(req))
#Login
def login(req):
  if  == 'POST':
    uf = UserForm()
    if uf.is_valid():
      # Get form user password
      username = uf.cleaned_data['username']
      password = uf.cleaned_data['password']
      #Comparison of form data retrieved with the database
      user = (username__exact = username,password__exact = password)
      if user:
        # Compare successfully, jump to index
        response = HttpResponseRedirect('/online/index/')
        # Write username to browser cookie, expiration time is 3600
        response.set_cookie('username',username,3600)
        return response
      else:
        #Rather failing, still logging in
        return HttpResponseRedirect('/online/login/')
  else:
    uf = UserForm()
  return render_to_response('',{'uf':uf},context_instance=RequestContext(req))
#Login successful
def index(req):
  username = ('username','')
  return render_to_response('' ,{'username':username})
#Exit
def logout(req):
  response = HttpResponse('logout !!')
  #Clean up the cookie that holds the username.
  response.delete_cookie('username')
  return response