如何在ReadTheDocs中将matplotlib的plot-directive与python-3一起使用？

我有一个python-3项目，该项目使用plot指令即时生成和嵌入matplotlib的图，并且使用ReadTheDocs自动生成该项目的文档。在python-2中，
plot-directive确实可以正常工作，但目前在python-3中失败。

具体来说，我在RTD日志中遇到的故障是：

建立标准错误

html
-----

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/wltp/envs/master/lib/python3.4/site-packages/sphinx/application.py", line 325, in setup_extension
    mod = __import__(extension, None, None, ['setup'])
ImportError: No module named 'matplotlib'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/wltp/envs/master/lib/python3.4/site-packages/sphinx/cmdline.py", line 253, in main
    warningiserror, tags, verbosity, parallel)
  File "/home/docs/checkouts/readthedocs.org/user_builds/wltp/envs/master/lib/python3.4/site-packages/sphinx/application.py", line 119, in __init__
    self.setup_extension(extension)
  File "/home/docs/checkouts/readthedocs.org/user_builds/wltp/envs/master/lib/python3.4/site-packages/sphinx/application.py", line 328, in setup_extension
    err)
sphinx.errors.ExtensionError: Could not import extension matplotlib.sphinxext.plot_directive (exception: No module named 'matplotlib')

Extension error:
Could not import extension matplotlib.sphinxext.plot_directive (exception: No module named 'matplotlib')

罪魁祸首可以追溯到由于遗忘了“ freetype” C库而未编译的matplotlib：

设定输出

...

requirements
-----
...
BUILDING MATPLOTLIB
            matplotlib: yes [1.4.2]
                python: yes [3.4.0 (default, Apr 11 2014, 13:05:11)  [GCC
                        4.8.2]]
              platform: yes [linux]

REQUIRED DEPENDENCIES AND EXTENSIONS
                 numpy: yes [not found. pip may install it below.]
                   six: yes [six was not found.]
              dateutil: yes [dateutil was not found. It is required for date
                        axis support. pip/easy_install may attempt to
                        install it after matplotlib.]
                  pytz: yes [pytz was not found. pip will attempt to install
                        it after matplotlib.]
               tornado: yes [tornado was not found. It is required for the
                        WebAgg backend. pip/easy_install may attempt to
                        install it after matplotlib.]
             pyparsing: yes [pyparsing was not found. It is required for
                        mathtext support. pip/easy_install may attempt to
                        install it after matplotlib.]
                 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.]
              freetype: no  [The C/C++ header for freetype2 (ft2build.h)
                        could not be found.  You may need to install the
                        development package.]    
    OPTIONAL LATEX DEPENDENCIES
                dvipng: yes [version 1.14]
           ghostscript: yes [version 9.10]
                 latex: yes [version 3.1415926]
               pdftops: no

============================================================================
                        * The following required packages can not be built:
                        * freetype

为了使文档生成过程顺利进行，我不得不按照RTD FAQ中的说明，使用./conf.py文件中的以下代码，通过模拟来“禁用”绘图指令。

我尝试了各种组合virtualenv（具有或不具有站点包可见性），特定requirements.txt于rtd的方法，但均未成功。

有没有人找到办法？

这些是那些愿意进一步研究该问题的提示：

• RTD上预安装的本机库的“官方”列表
• 从RTD的源代码中找到的用于设置构建服务器的实际pip-requirements.txt文件。