如何使用pip3安装pysaxon？

Question

我尝试使用下一种方式将库安装到我的项目中：

pip3 install -r requirements.txt

我的requirements.txt包含：

six
Cython
git+https://github.com/ajelenak/pysaxon.git

但是安装失败了：

Collecting git+https://github.com/ajelenak/pysaxon.git (from -r /var/www/gost/gost/requirements.txt (line 20))
  Cloning https://github.com/ajelenak/pysaxon.git to /tmp/pip-zkz6pq1u-build
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-zkz6pq1u-build/setup.py", line 8, in <module>
        from Cython.Build import cythonize
    ImportError: No module named 'Cython'

有什么问题？