form.is_valid（）返回false

Question

我从这个视图中得到了这段代码。我无法弄清楚为什么is_valid（）返回false，因此没有返回httpresponse。

class PostTweet(View):
    """Tweet Post form available on page /user/<username> URL"""
    def post(self, request, username):

        if request.method == 'POST':
            form = TweetForm(request.POST)
            if form.is_valid():
                user = User.objects.get(username=username)
                tweet = Tweet(text=form.cleaned_data['text'],
                user=user,country=form.cleaned_data['country'])
                tweet.save()
                words = form.cleaned_data['text'].split(" ")
                for word in words:
                    if word[0] == "#":
                        hashtag = HashTag.objects.get_or_create(name=word[1:])
                        hashtag.tweet.add(tweet)
                        return HttpResponseRedirect('/user/'+user)