pip在virtualen中安装matplotlib

Question

我想使用pip将matplotlib安装到virtualenv。（pip 7.1.0，python 3.4）

$ virtualenv venv
$ source venv/bin/activate
$ pip install matplotlib

...
REQUIRED DEPENDENCIES AND EXTENSIONS
                 numpy: yes [version 1.9.2]
                   six: yes [using six version 1.9.0]
              dateutil: yes [using dateutil version 2.4.2]
                  pytz: yes [using pytz version 2015.4]
               tornado: yes [using tornado version 4.2.1]
             pyparsing: yes [using pyparsing version 2.0.3]
                 pycxx: yes [Official versions of PyCXX are not compatible
                        with matplotlib on Python 3.x, since they lack
                        support for the buffer object.  Using local copy]
                libagg: yes [pkg-config information for 'libagg' could not
                        be found. Using local copy.]

我成功地安装了大部分依赖项，但是pycxx和libaag失败，并出现类似错误：

Collecting pycxx
  Could not find a version that satisfies the requirement pycxx (from versions: )
No matching distribution found for pycxx

我的问题是：我做错了什么？有办法吗？

我可以（也许）使用发行版包管理器安装matplotlib，然后以某种方式将其导入virtualenv——这就是我需要帮助的地方。