try and if - local variable referenced before assignment

Question

I tried run this code but I have an error:

a4 local variable referenced before assignment

a1 = '/fr/store/a'
try:
   a2 = '/fr/store/b/collection/3432'
   a2_store = "store"
   a3 = a2.split ("store/")
   a4 = a3[0]
   if a2_store in a2:
      print ('a2')
except:
   if a4 not in a1:
      print ('a1')

Answer 1

If an exception is raised before a4 = a3[0] is executed (for example, if a3[0] raises an IndexError ), then a4 is, indeed, not defined.