New submission from Andy Friesen <[email protected]>:
In certain circumstances, "if __debug__" seems to be evaluating its "else"
clause even when -O is not specified. This can cause very surprising behavior.
a.zip contains a single file named a/__init__.pyo. It is the compiled form of
the following code:
if __debug__:
print 'DEBUG'
else:
print 'RELEASE'
if __debug__ == True:
raise Exception("this is impossible")
pythonbug.py evaluates this script with the following:
import sys
sys.path = ['a.zip']
import a
When using Windows Python 2.6.2 and 2.6.5, running pythonbug.py produces this
output:
RELEASE
Traceback (most recent call last):
File "pythonbug.py", line 3, in <module>
import a
File "__init__.py", line 8, in <module>
raise Exception("this is impossible")
Exception: this is impossible
When -O is passed, the exception is not raised.
My best guess is that the Python bytecode is optimizing the "if __debug__" test
away in the produced .pyo, but does not actually affect the value of __debug__
or check more complex expressions involving __debug__.
----------
files: pythonbug.zip
messages: 102975
nosy: afriesen
severity: normal
status: open
title: if __debug__: has nonobvious behaviour when evaluating .pyo without -O
type: behavior
versions: Python 2.6
Added file: http://bugs.python.org/file16901/pythonbug.zip
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Python tracker <[email protected]>
<http://bugs.python.org/issue8379>
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