Repository navigation
__debug__ in compile(optimize=1) #66289
Description
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
Show more details
GitHub fields:
assignee = None
closed_at = <Date 2017-12-15.11:28:34.891>
created_at = <Date 2014-07-27.11:32:00.282>
labels = ['interpreter-core', 'type-bug', '3.7']
title = '__debug__ in compile(optimize=1)'
updated_at = <Date 2017-12-15.11:28:34.888>
user = 'https://github.com/arigo'bugs.python.org fields:
activity = <Date 2017-12-15.11:28:34.888>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2017-12-15.11:28:34.891>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2014-07-27.11:32:00.282>
creator = 'arigo'
dependencies = []
files = []
hgrepos = []
issue_num = 22091
keywords = ['patch']
message_count = 9.0
messages = ['224119', '224120', '224126', '266770', '308377', '308379', '308380', '308382', '308384']
nosy_count = 6.0
nosy_names = ['arigo', 'vstinner', 'SilentGhost', 'serhiy.storchaka', 'eryksun', 'josh.r']
pr_nums = ['4880', '4882']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue22091'
versions = ['Python 3.6', 'Python 3.7']
Activity
arigo commentedon Jul 27, 2014
The documentation of the built-in compile() function is not 100% clear but I think it says that giving the "optimize=1" argument turns "__debug__" to false in the compiled code ( https://docs.python.org/3.5/library/functions.html?highlight=compile#compile ). It doesn't work this way in practice, though:
python3.5 >>> exec(compile("print(__debug__)", "exec", "exec", optimize=1)) TrueI'd recommend to fix either the documentation or the source code.
SilentGhost commentedon Jul 27, 2014
I can reproduce your example on 3.4, but for the comparison:
So, it's not as straightforward as one might imagine.
eryksun commentedon Jul 27, 2014
If __debug__ were referenced from the code object's co_consts instead of checking locals, globals and builtins (LOAD_NAME), then optimize=1 would work consistently for a given code object.
Currently in 3.4.1:
>>> dis.dis(compile("if __debug__: x = 1", "", "exec", optimize=0)) 1 0 LOAD_CONST 0 (1) 3 STORE_NAME 0 (x) 6 LOAD_CONST 1 (None) 9 RETURN_VALUE >>> dis.dis(compile("if __debug__: x = 1", "", "exec", optimize=1)) 1 0 LOAD_CONST 0 (None) 3 RETURN_VALUE >>> dis.dis(compile("x = __debug__", "", "exec", optimize=0)) 1 0 LOAD_NAME 0 (__debug__) 3 STORE_NAME 1 (x) 6 LOAD_CONST 0 (None) 9 RETURN_VALUE >>> dis.dis(compile("x = __debug__", "", "exec", optimize=1)) 1 0 LOAD_NAME 0 (__debug__) 3 STORE_NAME 1 (x) 6 LOAD_CONST 0 (None) 9 RETURN_VALUEWith the current design, an exec can override builtins.__debug__ in globals or locals:
>>> exec("print(__debug__)", globals(), {"__debug__": "spam"}) spamMojoVampire commentedon May 31, 2016
I just opened bpo-27169: "__debug__ is not optimized out at compile time for anything but `if:` and `while:` blocks" as a more general case of this bug.
This bug covers inconsistent behavior, but ultimately, it's caused by incomplete optimization: `__debug__` doesn't act as a compile time constant outside of `if:` and `while:` blocks, so the behavior is inconsistent for all other uses in the `compile` case where `optimize` doesn't match the main interpreter session, and inefficient for all other uses whether or not `compile` is involved.
If bpo-27169 is resolved as I suggested (or in some other similar way), it would also resolve this bug.
serhiy-storchaka commentedon Dec 15, 2017
New changeset 3325a67 by Serhiy Storchaka in branch 'master':
bpo-27169: The __debug__ constant is now optimized out at compile time. (bpo-4880)
3325a67
serhiy-storchaka commentedon Dec 15, 2017
Is it worth to backport this change?
vstinner commentedon Dec 15, 2017
It's an optimization, usually the answer is no.
The change is short and can be seen as a bugfix, so it's up to you, it's ok to backport to 3.6, and maybe even 2.7, if it's not too hard to write the backport.
serhiy-storchaka commentedon Dec 15, 2017
New changeset b82da9e by Serhiy Storchaka in branch '3.6':
[3.6] bpo-27169: The __debug__ constant is now optimized out at compile time. (GH-4880) (bpo-4882)
b82da9e
serhiy-storchaka commentedon Dec 15, 2017
The backport to 3.6 is straightforward, but backporting to 2.7 would require larger changes.