I create a template following django's document:

< h1 > {{poll.question}} h1 >
{%if error_message%} < p >< strong > {{error_message}} strong > p > {%endif%}

 < form  action ="/polls/{{poll.id}}/vote"  method ="post" >
    {%for choice in poll.get_choice_list%}
         < input  type ="radio"  name ="choice"  id ="choice{{forloop.counter}}"  value ="{{choice.id}}" />
         < label  for ="choice{{forloop.counter}}" > {{choice.choice}} label >< br />
    {%endfor%}
     < input  type ="submit"  value ="Vote" >
form >

And try to get params from post in python:

def  vote(request, poll_id):
    p  =  get_object_or_404(polls, pk = poll_id)
     print  request.GET
     print  request.POST    
     return  HttpResponseRedirect( ' /polls/%s/results/ '   %  p.id)

But the result was null:(

{}
{}

While I change the method to get

< form  action ="/polls/{{poll.id}}/vote"  method ="get" >

I can get the params's value.
{'choice': ['1']}
{}

I don't know why,I wanna help!