[Django]-Django return HttpResponseRedirect to an url with a parameter

This should not be complicated. The argument to HttpResponseRedirect is simply a string, so the normal rules for building up a string apply here. However, I don’t think you want the theclass variable in there, as that is a ClassRoom object, not a string. You presumably want the classname instead. adamk has given you the right answer here.

However, having said that you can just use a string, what you should actually do is use the reverse function. This is because you might later decide to change the URL structure, and rather than having to look through your code finding each place you’ve hard-coded the URL string, you should rely on having defined them in one single place: your urls.py file. So you should do something like this:

from django.urls import reverse

url = reverse('notamember', kwargs={'classname': classname})
return HttpResponseRedirect(url)

Actually, the shortcut redirect takes view names and model (which has get_absolute_url defined) names too.

from django.shortcuts import redirect

return redirect(leave_classroom)

When everything seems not to be working i use return render and check if it is post request in case anybody refresh the page

if request.POST:
    message = "Thank you."
    return render(request, 'index.html', locals())
return HttpResponseRedirect('/')

The local() make the parameter accessible on the template

If you are submitting to the same URL, you can use the following to pass parameters.

 template_name = '/classroom/notamember.html'

return render(
                request,
                self.template_name,
                {'classname': 'classname', 'secondvariable': 'variable' }
            )