On 28/04/2011 09:34, Terry Reedy wrote:
On 4/28/2011 3:54 AM, Tarek Ziadé wrote:
Hello
I removed some assert calls in distutils some time ago because the
package was not behaving correctly when people were using Python with
the --optimize flag. In other words, assert became a full part of the
code logic and removing them via -O was changing the behavior.
In my opinion assert should be avoided completely anywhere else than
in the tests. If this is a wrong statement, please let me know why :)
My understanding is that assert can be used in production code but
only to catch logic errors by testing supposed invariants or
postconditions. It should not be used to test usage errors, including
preconditions. In other words, assert presence or absence should not
affect behavior unless the code has a bug.
Agreed. We should ideally have buildbots doing test runs with -O and
-OO. R. David Murray did a lot of work a year ago (or so) to ensure the
test run passes with -OO but it easily degrades..
There are a couple of asserts in unittest (for test discovery) but I
only use them to provide failure messages early. The functionality is
unchanged (and tests still pass) with -OO.
All the best,
Michael Foord
So, I grepped the stdlib for assert calls, and I have found 177 of
them and many of them are making Python acts differently depending on
the -O flag,
Here's an example on a randomly picked assert in the threading module:
This, to me is wrong:
def __init__(self, group=None, target=None, name=None,
args=(), kwargs=None, verbose=None):
assert group is None, "group argument must be None for now"
That catches a usage error and should raise a ValueError.
This
def _wait(self, timeout):
if not self._cond.wait_for(lambda : self._state != 0, timeout):
#timed out. Break the barrier
self._break()
raise BrokenBarrierError
if self._state < 0:
raise BrokenBarrierError
assert self._state == 1
appears to be, or should be, a test of a postcondition that should
*always* be true regardless of usage.
--
http://www.voidspace.org.uk/
May you do good and not evil
May you find forgiveness for yourself and forgive others
May you share freely, never taking more than you give.
-- the sqlite blessing http://www.sqlite.org/different.html
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