我尝试在我们的本地 pypi 服务器上安装 icalendar：
第一次尝试失败，现在我知道我需要对 pytz 使用 --pre。但是仍然找不到依赖项：
(pypi)pypi@gray:~> pip install --pre -d packages pytz
Downloading/unpacking pytz
Downloading pytz-2013d.tar.bz2 (204kB): 204kB downloaded
Saved ./packages/pytz-2013d.tar.bz2
Running setup.py egg_info for package pytz
warning: no files found matching '*.pot' under directory 'pytz'
warning: no previously-included files found matching 'test_zdump.py'
Successfully downloaded pytz
Cleaning up...
现在我尝试安装icalendar：
(pypi)pypi@gray:~> pip install -d packages icalendar
Downloading/unpacking icalendar
File was already downloaded packages/icalendar-3.5.tar.gz
Running setup.py egg_info for package icalendar
warning: no previously-included files matching '*.pyc' found under directory 'src/icalendar'
Downloading/unpacking setuptools (from icalendar)
File was already downloaded packages/setuptools-1.1.5.tar.gz
Running setup.py egg_info for package setuptools
Downloading/unpacking python-dateutil (from icalendar)
File was already downloaded packages/python-dateutil-2.1.tar.gz
Running setup.py egg_info for package python-dateutil
Downloading/unpacking pytz (from icalendar)
Could not find a version that satisfies the requirement pytz (from icalendar) (from versions: 2010b, 2012f, 2010e, 2005m, 2011e, 2010l, 2010e, 2009u, 2008c, 2006j,... 2013d, 2013d, 2012h, 2011h, 2013b, 2012d, 2004b)
Cleaning up...
No distributions matching the version for pytz (from icalendar)
Storing complete log in /home/pypi/.pip/pip.log
任何提示如何解决这个问题？