Python tricks

RajNewbie raj.indian.08 at gmail.com
Mon Jan 12 14:10:45 CET 2009


Hi,
   My code has a lot of while loops of the following format:
   while True:
     ...
     if <condition>: break

   The danger with such a code is that it might go to an infinite loop
- if the <condition> never occurs.
   Is there a way - a python trick - to have a check such that if the
loop goes for more than x number of steps, it will cause an exception?

   I do understand that we can use the code like -
   i = 0
   while True:
     i++
     if i > 200: raise infinite_Loop_Exception
     ...
     if <condition>: break

   But I am not very happy with this code for 3 reasons
   1. Verbosity (i=0 and i++) which doesnt add to the logic
   2. The loop now has dual focus. - incrementing i, etc.
   3. <most important>   A person looks into the code and thinks 'i'
has special significance. His/her mind will be focused on not the
actual reason for the loop.

   The solution that I had in mind is:
   while True:
     ...
     if <condition>: break
     if inifinte_loop(): raise infiinte_loop_exception

  Wherein infinite_loop is a generator, which returns true if i > 200
  def infinite_loop():
     i = 0
     while i < 200:
         i++
         yield False
     yield True

Could somebody let me know whether this is a good option?
    One of my main worries is - what will happen if I call this same
procedure from another loop? Will it start again from 0 or will it
again start from my previous stored i? i.e.
def big_proc:
  while True:
   ...
   if infinite_loop: raise

  while True:
    ...
   if infinite_loop: raise
In such a case, will we run it 200 times both the times or not?

Could someone chip in with other suggestions?



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