try exception 捕获异常

a=1
b=2
try:
  a/b
  print 2222
except:
  print 3333


C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/mycompany/thread/p12.py
2222

a=1
b=0
try:
  a/b
  print 2222
except:
  print 3333

C:Python27python.exe C:/Users/TLCB/PycharmProjects/untitled/mycompany/thread/p12.py
3333



def main(req):
      print req.session
      try:
        a=req.session['username']
        return render_to_response('login.html')
      except:
          return redirect('/index/')