On Oct 11, 2009, at 5:51 PM, bartc wrote:
Mensanator wrote:
On Oct 10, 3:15�pm, kj <no.em...@please.post> 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"?
If you know this "exit that is always reached",
why do you pretend not to know it by writing
"while True"?
When I'm starting to code something I haven't yet fully worked out,
it often starts with an infinite loop like this, until the body is
coded and I've figured out how to escape from it.
At the end if may or may not be tidied up, depending on how much
work it is to reconcile several possible break points into a single
terminating condition to be place at one end, and whether that is
likely to break or obfuscate a currently working program.
But if it's never going to be seen by the brigade who hate all
break, exit, goto and multiple return statements, then I won't bother.
I think you bring up a good point. I think "while True" has some
legitimate uses (like event loops), and I don't mind seeing it there.
What I don't like is goto, and to a lesser extent break, exit, and
multiple returns. I don't find too many cases where they're the
clearest way to express things. And where one sees a "while True", one
can almost always find a "break" or two lurking in the loop.
IMHO, break, goto, etc. have their place, but they're ripe for abuse
which leads to spaghetti code. Since the OP is teaching non-
programmers to write code, I think the potential for abuse is
especially important to keep in mind. I'd think that teaching them a
tool like "while True" would encourage the "code now, design later"
trap that even experienced programmers -- including myself --
sometimes fall into. Writing "while <condition>" instead forces one to
stop at the beginning of the loop and think at least a little about
exactly what it's meant to accomplish.
In addition, isn't it easier to figure out how this loop ends --
while (condition1) and (condition2) and (condition3):
...lots of code here...
than this one?
while True:
...lots of code here...
if not condition1:
break
...lots of code here...
if not condition2:
break
...lots of code here...
if not condition3:
break
My $.02,
Philip
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