Updated venv documentation with an example.
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Vinay Sajip
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@ -178,3 +178,216 @@ There is also a module-level convenience function:
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Create an :class:`EnvBuilder` with the given keyword arguments, and call its
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:meth:`~EnvBuilder.create` method with the *env_dir* argument.
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An example of extending ``EnvBuilder``
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--------------------------------------
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The following script shows how to extend :class:`EnvBuilder` by implementing a
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subclass which installs Distribute and pip into a created venv::
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import os
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import os.path
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from subprocess import Popen, PIPE
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import sys
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from threading import Thread
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from urllib.parse import urlparse
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from urllib.request import urlretrieve
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import venv
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class DistributeEnvBuilder(venv.EnvBuilder):
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"""
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This builder installs Distribute and pip so that you can pip or
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easy_install other packages into the created environment.
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:param nodist: If True, Distribute is not installed into the created
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environment.
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:param nopip: If True, pip is not installed into the created
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environment.
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:param progress: If Distribute or pip are installed, the progress of the
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installation can be monitored by passing a progress
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callable. If specified, it is called with two
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arguments: a string indicating some progress, and a
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context indicating where the string is coming from.
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The context argument can have one of three values:
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'main', indicating that it is called from virtualize()
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itself, and 'stdout' and 'stderr', which are obtained
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by reading lines from the output streams of a subprocess
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which is used to install the app.
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If a callable is not specified, default progress
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information is output to sys.stderr.
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"""
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def __init__(self, *args, **kwargs):
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self.nodist = kwargs.pop('nodist', False)
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self.nopip = kwargs.pop('nopip', False)
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self.progress = kwargs.pop('progress', None)
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self.verbose = kwargs.pop('verbose', False)
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super().__init__(*args, **kwargs)
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def post_setup(self, context):
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"""
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Set up any packages which need to be pre-installed into the
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environment being created.
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:param context: The information for the environment creation request
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being processed.
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"""
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if not self.nodist:
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self.install_distribute(context)
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if not self.nopip:
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self.install_pip(context)
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def reader(self, stream, context):
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"""
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Read lines from a subprocess' output stream and either pass to a progress
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callable (if specified) or write progress information to sys.stderr.
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"""
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progress = self.progress
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while True:
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s = stream.readline()
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if not s:
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break
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if progress is not None:
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progress(s, context)
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else:
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if not self.verbose:
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sys.stderr.write('.')
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else:
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sys.stderr.write(s.decode('utf-8'))
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sys.stderr.flush()
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def install_script(self, context, name, url):
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_, _, path, _, _, _ = urlparse(url)
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fn = os.path.split(path)[-1]
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binpath = context.bin_path
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distpath = os.path.join(binpath, fn)
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# Download script into the env's binaries folder
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urlretrieve(url, distpath)
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progress = self.progress
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if progress is not None:
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progress('Installing %s' %name, 'main')
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else:
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sys.stderr.write('Installing %s ' % name)
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sys.stderr.flush()
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# Install in the env
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args = [context.env_exe, fn]
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p = Popen(args, stdout=PIPE, stderr=PIPE, cwd=binpath)
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t1 = Thread(target=self.reader, args=(p.stdout, 'stdout'))
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t1.start()
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t2 = Thread(target=self.reader, args=(p.stderr, 'stderr'))
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t2.start()
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p.wait()
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t1.join()
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t2.join()
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if progress is not None:
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progress('done.', 'main')
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else:
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sys.stderr.write('done.\n')
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# Clean up - no longer needed
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os.unlink(distpath)
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def install_distribute(self, context):
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"""
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Install Distribute in the environment.
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:param context: The information for the environment creation request
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being processed.
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"""
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url = 'http://python-distribute.org/distribute_setup.py'
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self.install_script(context, 'distribute', url)
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# clear up the distribute archive which gets downloaded
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pred = lambda o: o.startswith('distribute-') and o.endswith('.tar.gz')
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files = filter(pred, os.listdir(context.bin_path))
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for f in files:
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f = os.path.join(context.bin_path, f)
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os.unlink(f)
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def install_pip(self, context):
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"""
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Install pip in the environment.
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:param context: The information for the environment creation request
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being processed.
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"""
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url = 'https://raw.github.com/pypa/pip/master/contrib/get-pip.py'
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self.install_script(context, 'pip', url)
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def main(args=None):
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compatible = True
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if sys.version_info < (3, 3):
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compatible = False
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elif not hasattr(sys, 'base_prefix'):
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compatible = False
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if not compatible:
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raise ValueError('This script is only for use with '
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'Python 3.3 or later')
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else:
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import argparse
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parser = argparse.ArgumentParser(prog=__name__,
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description='Creates virtual Python '
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'environments in one or '
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'more target '
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'directories.')
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parser.add_argument('dirs', metavar='ENV_DIR', nargs='+',
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help='A directory to create the environment in.')
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parser.add_argument('--no-distribute', default=False,
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action='store_true', dest='nodist',
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help="Don't install Distribute in the virtual "
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"environment.")
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parser.add_argument('--no-pip', default=False,
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action='store_true', dest='nopip',
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help="Don't install pip in the virtual "
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"environment.")
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parser.add_argument('--system-site-packages', default=False,
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action='store_true', dest='system_site',
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help='Give the virtual environment access to the '
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'system site-packages dir.')
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if os.name == 'nt':
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use_symlinks = False
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else:
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use_symlinks = True
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parser.add_argument('--symlinks', default=use_symlinks,
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action='store_true', dest='symlinks',
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help='Try to use symlinks rather than copies, '
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'when symlinks are not the default for '
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'the platform.')
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parser.add_argument('--clear', default=False, action='store_true',
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dest='clear', help='Delete the contents of the '
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'environment directory if it '
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'already exists, before '
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'environment creation.')
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parser.add_argument('--upgrade', default=False, action='store_true',
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dest='upgrade', help='Upgrade the environment '
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'directory to use this version '
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'of Python, assuming Python '
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'has been upgraded in-place.')
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parser.add_argument('--verbose', default=False, action='store_true',
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dest='verbose', help='Display the output '
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'from the scripts which '
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'install Distribute and pip.')
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options = parser.parse_args(args)
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if options.upgrade and options.clear:
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raise ValueError('you cannot supply --upgrade and --clear together.')
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builder = DistributeEnvBuilder(system_site_packages=options.system_site,
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clear=options.clear,
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symlinks=options.symlinks,
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upgrade=options.upgrade,
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nodist=options.nodist,
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nopip=options.nopip,
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verbose=options.verbose)
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for d in options.dirs:
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builder.create(d)
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if __name__ == '__main__':
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rc = 1
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try:
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main()
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rc = 0
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except Exception as e:
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print('Error: %s' % e, file=sys.stderr)
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sys.exit(rc)
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This script is also available for download `online
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<https://gist.github.com/4673395>`_.
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