I can understand the desire for correctness. I do have to wonder though: has anyone *other* than language implementors noticed this issue with SyntaxErrors not being reported?
Perhaps we should remember "Practicality beats purity"?
--Ned.
On 7/5/19 6:14 PM, Pablo Galindo Salgado wrote:
> 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.
On Fri, 5 Jul 2019 at 23:10, Victor Stinner <vstinner@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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