Mailman 3 December 2012 - Edu-sig

a short essay about programming
by kirby urner 08 Dec '22

08 Dec '22

A common "error" (not too serious) that I see in beginning Python (and no doubt other languages, but Python is the one I'm teaching), is having a while condition that appears to put a lid on things, but then the flow all leaks away through break statements, such that the "front door" condition is never revisited. while guess != secret: guess = int(input("Guess?: ") if guess == secret: print("You guessed it!") break else: print("Nope, try again...") What's messed up about the above code is you never really go back to the top in the case where you'd get to leave. Rather, you exit by the back door, through break. So in that case, wouldn't have been simpler and more elegant, even more "correct" (dare I say it) to have gone: while True: # no ifs ands or buts guess = int(input("Guess?: ") if guess == secret: print("You guessed it!") break else: print("Nope, try again...") I see lots of heads nodding, and that could be the end of the matter, but then a next question arises: wouldn't this also be a more correct solution?: while guess != secret: guess = int(input("Guess?: ") if guess == secret: print("You guessed it!") continue # instead of break else: print("Nope, try again...") We're back to having a variable while condition, not a boolean constant, but this time we actually exit by means of it, thanks to continue or... while guess != secret: guess = int(input("Guess?: ") if guess == secret: print("You guessed it!") else: print("Nope, try again...") ... thanks to no continue. This last one is getting a thumbs up, but then I'd pause here and say "continue" can be easier on the eyes. It's unambiguous where it takes you, in contrast to having to scan on down the gauntlet, looking for possibly other open doors. "What happens next" should not require scanning ahead too far. Help us not to get lost. Be a civic-minded coder. I'm thinking of a programming style that advises two things: (a) if you use a while condition that's variable, that's expected to change, then your goal should be to always exit because of that, i.e. that should be your only exit point. Even if some other criterion suggests exiting, you have the option to flip that "lid" at the top, to crack that front door, and bounce the ball out. (b) which is why 'continue' is your friend. You are showing the user where your 'break' statements are, except you don't use "break" statements, as you've given a non-constant condition, and your aim is to make that your ONLY exit point. In short: never use break to exit a while loop unless your condition is while True. Instead, always flip the condition and exit through the font door. However, as soon as I make that rule I can think of good reasons to break it. The other programmers in the room are shaking their heads. Won't we lose information, needed elsewhere in the program, if we "artificially" force a True condition to False. Aren't we, in effect, lying? That concern could be addressed. Keep all the info true, just treat the "lid condition" (it "keeps a lid on it") as a flag. Go ahead and remember the user's guess. allowed = 5 tries = 1 exit = False while not exit: # no other way out guess = int(input("Guess?: ") if guess == secret: print("You guessed it!") exit = True # instead of break continue print("Nope, try again...") tries += 1 if tries == allowed: print("You've maxed out") exit = True continue I think we all understand the main issue: writing reader-friendly code, and rules for doing so. There's something comforting about approaching a while loop and knowing its not a leaky sieve, riddled with back doors, maybe even an exit( ) time bomb. But in the recursion world we want a minimum of two exits usually: when another round is called for versus when we've "hit bottom". Can we have it both ways? Conclusions: Lets not be too hasty with rules of thumb and: Lets keep the reader in mind when writing code. Just because the interpreter knows to compute the flow unambiguously, doesn't mean all ways of writing it are equally reader-friendly. What may seem a gratuitous gesture, an unnecessary flourish, may actually promote reader comprehension of your code, and that should be a goal as much as satisfying the interpreter. Kirby

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Re: [Edu-sig] RurPLE-NG is nice
by Jurgis Pralgauskis 05 Apr '14

05 Apr '14

Some updates: - separated Variables Watch and Output panes, to be seen simultaneusly - implemented Breakpoints :) - beta style Todo: - let enter arbitrary watch expressions http://ftp.akl.lt/users/jurgis/python/rurple-NG053.png http://ftp.akl.lt/users/jurgis/python/rurple-ng-dz0-SplitLogVars_and_Breakp… for windows one doesn't need to install python separately, just unzip and run :) http://ftp.akl.lt/users/jurgis/python/RURPLE-NG-0.53%20%5bindependent%20exe… ps.: RurPLE-NG uses py3 unicode_literals, with_statement, division, print_function so code is generally py3 compliant. when wxpy will work well with py3 it shouldn't be too hard to port fully... >> >> just wanted to mention, >> that http://dev.lshift.net/paul/rurple/ >> is a very nice and lightweit PLE. >> >> what I like most (compared to RurPLE) are: >> 1) variables watch list (if it had breakpoints, it would rock :)

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Re: [Edu-sig] Edu-sig Digest, Vol 113, Issue 18
by Marianne McKenna 31 Dec '12

31 Dec '12

I will be out of the office for the holiday break. I will be checking email periodically and will respond as soon as I can. If you need immediate help please contact the computer center. Thanks.

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Re: [Edu-sig] Edu-sig Digest, Vol 113, Issue 17
by Marianne McKenna 30 Dec '12

30 Dec '12

I will be out of the office for the holiday break. I will be checking email periodically and will respond as soon as I can. If you need immediate help please contact the computer center. Thanks.

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Re: [Edu-sig] Edu-sig Digest, Vol 113, Issue 16
by Marianne McKenna 29 Dec '12

29 Dec '12

I will be out of the office for the holiday break. I will be checking email periodically and will respond as soon as I can. If you need immediate help please contact the computer center. Thanks.

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Re: [Edu-sig] Edu-sig Digest, Vol 113, Issue 14
by Daniel Ajoy 28 Dec '12

28 Dec '12

+1 On Fri, 28 Dec 2012 06:00:01 -0500, <edu-sig-request(a)python.org> wrote: > Once again, can someone please unsubscribe this twit?

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Re: [Edu-sig] Edu-sig Digest, Vol 113, Issue 15
by Marianne McKenna 28 Dec '12

28 Dec '12

I will be out of the office for the holiday break. I will be checking email periodically and will respond as soon as I can. If you need immediate help please contact the computer center. Thanks.

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Re: [Edu-sig] Edu-sig Digest, Vol 113, Issue 14
by Marianne McKenna 27 Dec '12

27 Dec '12

I will be out of the office for the holiday break. I will be checking email periodically and will respond as soon as I can. If you need immediate help please contact the computer center. Thanks.

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Re: [Edu-sig] Edu-sig Digest, Vol 113, Issue 13
by Marianne McKenna 26 Dec '12

26 Dec '12

I will be out of the office for the holiday break. I will be checking email periodically and will respond as soon as I can. If you need immediate help please contact the computer center. Thanks.

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Fwd: [Chicago] Dr Chuck MOOC
by kirby urner 26 Dec '12

26 Dec '12

On my radar... ---------- Forwarded message ---------- From: Randy Baxley <randy7771026(a)gmail.com> Date: Sat, Dec 22, 2012 at 12:49 PM Subject: [Chicago] Dr Chuck MOOC To: chicago(a)python.org http://online.dr-chuck.com/index.php Dr. Chuck is a fun professor and I have already worked through his pythonlearn.com basics so this should be fun. Randy _______________________________________________ Chicago mailing list Chicago(a)python.org http://mail.python.org/mailman/listinfo/chicago

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