4 ms·

Same here, I often find myself writing a loop-and-a-half and will on occasion repeat expressions to get around extra lines (if I cared about performance, I woul

Same here, I often find myself writing a loop-and-a-half and will on occasion repeat expressions to get around extra lines (if I cared about performance, I wouldn't be writing it in Python). I feel like a lot of the resistance is from people who think this is somehow bad style, because it's associated with a source of bugs in other languages. The same kind of people will argue endlessly against having 'goto' in a language, even when it can clearly make for cleaner code (eat it, Dijkstra!) in some cases.

bogomipz 8y ago
Can you explain what a "loop-and-a-half" is in Python?
- blake_himself 8y ago
  x = stuff while x: x = stuff
  - Delgan 8y ago
    On the contrary, loop-and-a-half is intended to avoid repeating stuff outside and inside of the loop body. while true: x = stuff if not x: break
    - chucksmash 8y ago
      GPs example is perfectly valid as well - this is just a restatement of the same logic in a way that keeps the logic contained within the loop at the cost of using a conditional plus a break inside of an unconditional loop. See [0]: Another motivating code pattern is the "loop and a half". It was once common for processing a file by line, but that has been solved by making file objects iterable; however other non-iterable interfaces still suffer from patterns like: line = f.readline() while line: ... # process line line = f.readline() or like this: while True: line = f.readline() if not line: break ... # process line Either of those could be replaced with a much more clear and concise version using an assignment expression: while line := f.readline(): ... # process line [0]: https://lwn.net/Articles/757713/ https://lwn.net/Articles/757713/
sevensor 8y ago
I think EWD was basically in the right to push hard for structured programming, but I also like Knuth's nuanced take: https://pic.plover.com/knuth-GOTO.pdf https://pic.plover.com/knuth-GOTO.pdf

bogomipz 8y ago

Can you explain what a "loop-and-a-half" is in Python?

blake_himself 8y ago
x = stuff while x: x = stuff
- Delgan 8y ago
  On the contrary, loop-and-a-half is intended to avoid repeating stuff outside and inside of the loop body. while true: x = stuff if not x: break
  - chucksmash 8y ago
    GPs example is perfectly valid as well - this is just a restatement of the same logic in a way that keeps the logic contained within the loop at the cost of using a conditional plus a break inside of an unconditional loop. See [0]: Another motivating code pattern is the "loop and a half". It was once common for processing a file by line, but that has been solved by making file objects iterable; however other non-iterable interfaces still suffer from patterns like: line = f.readline() while line: ... # process line line = f.readline() or like this: while True: line = f.readline() if not line: break ... # process line Either of those could be replaced with a much more clear and concise version using an assignment expression: while line := f.readline(): ... # process line [0]: https://lwn.net/Articles/757713/ https://lwn.net/Articles/757713/

sevensor 8y ago

I think EWD was basically in the right to push hard for structured programming, but I also like Knuth's nuanced take: https://pic.plover.com/knuth-GOTO.pdf https://pic.plover.com/knuth-GOTO.pdf