c1.list_budget[choose_cat].append(a2) AttributeError: 'int' object has no attribute 'append'

Question

When I try to run this below code then following error occur and I am new at Python programming. Please tell me the solution.

Thanks

c1 = Category()
c1.cat_print()
choose_cat = int(input("Choose category Between 0 To 4: "))
a1 = c1.list_category[choose_cat]
amount = int(input("Enter Amount: "))
a2 = c1.list_budget[choose_cat] + amount
c1.list_budget[choose_cat].append(a2)
print(a1, a2)
note = input("Enter Note: ")
print(amount, choose_cat, note)