[Distutils] OS X problem with pkg_resources and the twisted event loop

[Michael Twomey]

Hi,

I've come across a problem with an easy_install managed package
(matplotlib) on my OS X box. When I try to import it for the first
time inside of a twisted application I get this nasty traceback:

Traceback (most recent call last):
  File "/Users/mtt/Desktop/twisted_macosx_vers.py", line 12, in ?
    reactor.run()
  File "/usr/local/lib/python2.4/site-packages/twisted/internet/posixbase.py",
line 206, in run
    self.mainLoop()
  File "/usr/local/lib/python2.4/site-packages/twisted/internet/posixbase.py",
line 214, in mainLoop
    self.runUntilCurrent()
--- <exception caught here> ---
  File "/usr/local/lib/python2.4/site-packages/twisted/internet/base.py",
line 541, in runUntilCurrent
    call.func(*call.args, **call.kw)
  File "/Users/mtt/Desktop/twisted_macosx_vers.py", line 4, in get_platform
    import pkg_resources
  File "/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/site-packages/setuptools-0.6a9-py2.4.egg/pkg_resources.py",
line 534, in ?
    class Environment(object):
  File "/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/site-packages/setuptools-0.6a9-py2.4.egg/pkg_resources.py",
line 537, in Environment
    def __init__(self,search_path=None,platform=get_platform(),python=PY_MAJOR):
  File "/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/site-packages/setuptools-0.6a9-py2.4.egg/pkg_resources.py",
line 147, in get_platform
    version = _macosx_vers()
  File "/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/site-packages/setuptools-0.6a9-py2.4.egg/pkg_resources.py",
line 126, in _macosx_vers
    info = os.popen('/usr/bin/sw_vers').read().splitlines()
exceptions.IOError: [Errno 4] Interrupted system call


This seems to be caused by twisted's signal handling, which breaks
os.popen (and subprocess), see this bug:
http://twistedmatrix.com/bugs/issue733

I've attached a simple test script which triggers the problem (most of
the time for me, you have to run it a few times as it doesn't always
crash).

I've got a work around though:

If I import pkg_resources before starting my twisted app it seems to
fix the problem. (I presume that get_platform's output is being kept
somewhere, Environment's __init__ args I think.)

cheers,
  Michael
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