On 10:29 pm, guido@python.org wrote:
On Sat, Feb 6, 2010 at 12:49 PM, Ezio Melotti <ezio.melotti@gmail.com> wrote:
In #7712 I was trying to change regrtest to always run the tests in a temporary CWD (e.g. /tmp/@test_1234_cwd/). The patches attached to the issue add a context manager that changes the CWD, and it works fine when I run ./python -m test.regrtest from trunk/. However, when I try from trunk/Lib/ it fails with ImportErrors (note that the latest patch by Florent Xicluna already tries to workaround the problem). The traceback points to "the_package = __import__(abstest, globals(), locals(), [])" in runtest_inner (in regrtest.py), and a "print __import__('test').__file__" there returns 'test/__init__.pyc'. This can be reproduced quite easily: [snip]
I haven't tried to repro this particular example, but the reason is that we don't want to have to call getpwd() on every import nor do we want to have some kind of in-process variable to cache the current directory. (getpwd() is relatively slow and can sometimes fail outright, and trying to cache it has a certain risk of being wrong.)
Assuming you mean os.getcwd(): exarkun@boson:~$ python -m timeit -s 'def f(): pass' 'f()' 10000000 loops, best of 3: 0.132 usec per loop exarkun@boson:~$ python -m timeit -s 'from os import getcwd' 'getcwd()' 1000000 loops, best of 3: 1.02 usec per loop exarkun@boson:~$ So it's about 7x more expensive than a no-op function call. I'd call this pretty quick. Compared to everything else that happens during an import, I'm not convinced this wouldn't be lost in the noise. I think it's at least worth implementing and measuring. Jean-Paul