Le jeudi 8 août 2013 22:29:00 UTC+2, Terry Reedy a écrit : > On 8/8/2013 7:41 AM, Chris Angelico wrote: > > > On Thu, Aug 8, 2013 at 7:20 AM, <wxjmfa...@gmail.com> wrote: > > >>>>> def z2(): > > >> ... letters = 'abc' > > >> ... while True: > > >> ... c = input('letter: ') > > >> ... if c not in letters: > > >> ... print('end, fin, Schluss') > > >> ... break > > >> ... else: > > >> ... print('do stuff') > > > > > > > > > Minor quibble: I don't like having a hard exit followed by an "else". > > > > Whereas I tend to prefer to have the two alternatives cleanly marked as > > alternatives by both being indented the same. > > > > Many alternatives are not so trivial as the above. I remember reading > > one snippet in the CPython codebase where the 'else' was omitted and the > > if clause subdivided into about three paths. It took at least a minute > > to determine that all paths terminated in such a way that there really > > was an inplied else. How much easier it would have been to read the code > > if the author had explicitly types the 'else'. > > > > > If the "if" branch will unconditionally quit the loop (with a break, > > > here, but could also be a return, a thrown exception, etc etc), I > > > would prefer to see the "else" removed and its code unindented one > > > level. Maybe this is just personal preference, though, learned from > > > assembly language programming where a "block if" looks something like > > > this: > > > > > > ; if x == y: > > > CMP x,y > > > JNZ .else > > > ; Code for "x == y" > > > JMP .endif > > > .else: > > > ; Code for "else" > > > .endif > > > > > > Putting an unconditional departure in the "x == y" branch makes the > > > "JMP .endif" redundant. > > > > Python is not assembly ;-). 3.3 effectively ignores the extraneous > > 'else:'. Either way, if the condition is false, control jumps to the > > second print. For what little it matters, the bytecode is the same length. > > > > def f(): > > while True: > > if a: > > b = 1 > > break > > else: > > b = 2 > > > > >>> dis(f) > > 2 0 SETUP_LOOP 25 (to 28) > > > > 3 >> 3 LOAD_GLOBAL 0 (a) > > 6 POP_JUMP_IF_FALSE 19 > > > > 4 9 LOAD_CONST 1 (1) > > 12 STORE_FAST 0 (b) > > > > 5 15 BREAK_LOOP > > 16 JUMP_ABSOLUTE 3 > > > > 7 >> 19 LOAD_CONST 2 (2) > > 22 STORE_FAST 0 (b) > > 25 JUMP_ABSOLUTE 3 > > >> 28 LOAD_CONST 0 (None) > > 31 RETURN_VALUE > > > > def f(): > > while True: > > if a: > > b = 1 > > break > > b = 2 > > > > >>> dis(f) > > 2 0 SETUP_LOOP 25 (to 28) > > > > 3 >> 3 LOAD_GLOBAL 0 (a) > > 6 POP_JUMP_IF_FALSE 19 > > > > 4 9 LOAD_CONST 1 (1) > > 12 STORE_FAST 0 (b) > > > > 5 15 BREAK_LOOP > > 16 JUMP_FORWARD 0 (to 19) > > > > 6 >> 19 LOAD_CONST 2 (2) > > 22 STORE_FAST 0 (b) > > 25 JUMP_ABSOLUTE 3 > > >> 28 LOAD_CONST 0 (None) > > 31 RETURN_VALUE > > > > -- > > Terry Jan Reedy
----- The problem of this guy is not at this level. His problem is more simply, he most probably does not understand how to build a correct, proper loop. "What I wanted to happen is when the user typed something ... ... would cause the program to stop ... " jmf -- http://mail.python.org/mailman/listinfo/python-list