The rap against "while True:" loops

Jack Norton jack at 0x6a.com
Wed Oct 14 20:51:11 CEST 2009


kj wrote:
>
> I'm coaching a group of biologists on basic Python scripting.  One
> of my charges mentioned that he had come across the advice never
> to use loops beginning with "while True".  Of course, that's one
> way to start an infinite loop, but this seems hardly a sufficient
> reason to avoid the construct altogether, as long as one includes
> an exit that is always reached.  (Actually, come to think of it,
> there are many situations in which a bona fide infinite loops
> (typically within a try: block) is the required construct, e.g.
> when implementing an event loop.)
>
> I use "while True"-loops often, and intend to continue doing this
> "while True", but I'm curious to know: how widespread is the
> injunction against such loops?  Has it reached the status of "best
> practice"?
>
> TIA!
>
> kynn
>   
This thread has gotten a lot of posts concerning programming practices 
and dogma alike.  I'd like to add a personal use of `while True:` that 
has nothing to do with either best practices or dogma. 
I use python a *lot* to do day-to-day tasks in an engineering lab.  I 
use it to control, log, or otherwise converse with rs232 based gear, as 
well as use it to back up or organize documents, etc... (lo and behold, 
I use this scripting language to write little scripts here and there).  
Don't get me wrong, I also write full blown control/logging apps with 
python, but that is only 10% of my usage. 
Whenever I need to quickly log something (serial output of a device) 
quickly, I find myself writing this in the python REPL:
import serial
comport = serial.Serial('COMx', timeout=1)
while True:
    get = comport.readline()
    f.open("blah", 'a')
    f.write(get)
    f.close()

It is short enough that I don't see the need to write my own module.  
Sometimes I even add a little regexp based filtering -- which adds 2 
lines total.  When I am done logging I just give 'er a CTRL-C and be 
done with it.  It is also a hell of a lot less buggy and error prone 
than hyperterminal, which my boss uses to do the same thing. 
I think this is a perfect example of `while True:` that works damn well, 
and there isn't anything that can replace its simplicity.  Programming 
practices be damned, it is invaluable, and I would recommend doing it in 
my situation to any person, regardless of programming experience. 
Food for thought.

-Jack



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