Question

Is it possible to prevent the for loop from proceeding to the next value in the list/iterator if a certain condition is satisfied?

lst = list('abcde')
for alphabet in lst:
  if some_condition:
     # somehow prevent the for loop from advancing so that in the
     # next iteration, the value of alphabet remains the same as it is now
  # do something

Answer 1

I don’t think you can (or should) do this with a regular for list-iterator. You may want to look at this as a case of a work queue and use a while loop:

work_stack = list('abcde')

prev_item = ''
while work_stack:
    item = work_stack.pop(0)
    print item
    if prev_item=='a' and item == 'b':
        work_stack.insert(0,item)
    prev_item = item