> Until a solution which makes everyone happy can be found, I suggest to move back to the status quo: revert the change.
>More people seems to expect "if 0: ..." to be removed, than people who care of syntax errors on "if 0". I don't think this is that clear. As Paul wrote on the issue this is the result of fixing a bug that has been open since 2008 (11 years), which itself was noticed independently, also in 2008 (#1875 and #1920, respectively). He also independently discovered the same issue last year when writing some tests for IPython. https://bugs.python.org/msg347394 On Fri, 5 Jul 2019 at 23:10, Victor Stinner <vstin...@redhat.com> wrote: > Hi, > > Until a solution which makes everyone happy can be found, I suggest to > move back to the status quo: revert the change. > > More people seems to expect "if 0: ..." to be removed, than people who > care of syntax errors on "if 0". > > -- > > Would it be possible to detect if the "if 0" block would raise a > syntax error, and only remove it if it doesn't raise a syntax error? > > That's the approach I chose in my fatoptimizer project which is > implemented as an AST optimizer: > > https://github.com/vstinner/fatoptimizer/blob/master/fatoptimizer/dead_code.py > > See the tests to see which cases are *not* optimized: > > https://github.com/vstinner/fatoptimizer/blob/master/test_fatoptimizer.py#L2428 > > Some examples (the "dead code elimitaiton" is not only about "if 0", > but also "while 0", dead code after return, etc.): > > self.check_dont_optimize(""" > def func(): > if 0: > yield > """) > > self.check_dont_optimize("while 1: x = 1") > > self.check_dont_optimize(""" > def func(obj): > return > if 0: > yield from obj > """) > > self.check_dont_optimize(""" > try: > pass > except Exception: > yield 3 > """) > > See also the doc: > https://fatoptimizer.readthedocs.io/en/latest/optimizations.html#dead-code > > -- > > About code coverage, it seems like -X noopt would help: > https://github.com/python/cpython/pull/13600 > > But I'm not sure anymore after Ned Batchelder wrote: > > "The real-word implications from my world are this: if your code has > "if 0:" clauses in it, and you measure its coverage, then because the > lines have not been optimized away, coverage.py will think the lines > are a possible execution path, and will be considered a miss because > they are not executed. This will reduce your coverage percentage." > https://bugs.python.org/issue37500#msg347362 > > Does it mean that coverage.py will report even more "false positive" > using -X noopt? > > Victor >
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