我正在尝试将matplotlib字体更改为helvetica，我想在PDF绘图中使用它。我尝试以下操作：import matplotlib

matplotlib.use('PDF')

import matplotlib.pylab as plt

from matplotlib import rc

plt.rcParams['ps.useafm'] = True

rc('font',**{'family':'sans-serif','sans-serif':['Helvetica']})

plt.rcParams['pdf.fonttype'] = 42

当我使用verbose debug运行代码时，出现错误：backend WXAgg version 2.8.10.1

/Library/Frameworks/Python.framework/Versions/6.2/lib/python2.6/site-packages/matplotlib/__init__.py:833: UserWarning: This call to matplotlib.use() has no effect

because the the backend has already been chosen;

matplotlib.use() must be called *before* pylab, matplotlib.pyplot,

or matplotlib.backends is imported for the first time.

findfont: Could not match :family=sans-serif:style=normal:variant=normal:weight=normal:stretch=normal:size=medium. Returning /Library/Frameworks/Python.framework/Versions/6.2/lib/python2.6/site-packages/matplotlib/mpl-data/fonts/ttf/Vera.ttf

Assigning font /F1 = /Library/Frameworks/Python.framework/Versions/6.2/lib/python2.6/site-packages/matplotlib/mpl-data/fonts/ttf/Vera.ttf

Embedding font /Library/Frameworks/Python.framework/Versions/6.2/lib/python2.6/site-packages/matplotlib/mpl-data/fonts/ttf/Vera.ttf

Writing TrueType font

显然它找不到海尔维蒂卡。我不知道为什么。我在mpl数据的afm目录中有Helvetica，当matplotlib启动时，它会读取并输出：createFontDict: /Library/Frameworks/Python.framework/Versions/6.2/lib/python2.6/site-packages/matplotlib/mpl-data/fonts/afm/Helvetica.afm

我还需要一个特殊的ttf Helvetica字体吗？如果是的话，我怎么才能拿到？我知道我的系统上有Helvetica，因为我在Illustrator和许多其他程序中看到它。

我正在使用热情的Python发行版，如下所示：$ python

Enthought Python Distribution -- http://www.enthought.com

Version: 6.2-2 (32-bit)

Python 2.6.5 |EPD 6.2-2 (32-bit)| (r265:79063, May 28 2010, 15:13:03)

[GCC 4.0.1 (Apple Inc. build 5488)] on darwin

Type "help", "copyright", "credits" or "license" for more information.

>>> import matplotlib

>>> matplotlib.__version__

'0.99.3'

你知道怎么解决吗？

谢谢。