Python - 非常奇怪的 sys.path 行为

Question

sys.path[0]的内容是 '/usr/lib/python2.7/dist-packages/wx-2.8-gtk2-unicode'。Python的文档说，这个应该是脚本的工作目录。你觉得这可能是什么情况呢？

当我在交互式解释器中运行Python，并执行 import sys; print sys.path[0]; 时，它打印出 ''，这看起来是对的。

但是当我的Python脚本是从一个perl脚本调用时，我得到的sys.path[0]的内容就是上面的那个。

其他信息：

• 我在使用Python 2.7。
• 我在Ubuntu 11.10 64位系统上。
• 我的工作目录应该是 /mnt/galaxyData/custom/MSG_toy。
• perl脚本和它调用的python脚本都在 /mnt/galaxyData/custom/MSG_toy/msg 目录下（这个msg目录是一个符号链接，如果这有关系的话）。

这是sys.path的所有内容：

['/usr/lib/python2.7/dist-packages/wx-2.8-gtk2-unicode',
 '/mnt/galaxyData/custom/msg',
 '/usr/local/lib/python2.7/dist-packages/bx_python-0.7.1-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/pip-1.0.2-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/amqplib-1.0.2-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/BeautifulSoup-3.2.0-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/boto-2.1.1-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/Fabric-1.3.2-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/ssh-1.7.9-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/ipython-0.11-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/Logbook-0.3-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/lxml-2.3.2-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/Mako-0.5.0-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/MarkupSafe-0.15-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/nose-1.1.2-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/numpy-1.6.1-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/Paste-1.7.5.1-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/PasteScript-1.7.5-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/PasteDeploy-1.5.0-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/python_cjson-1.0.5-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/pyOpenSSL-0.13-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/PyYAML-3.10-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/Routes-1.12.3-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/simplejson-2.2.1-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/Sphinx-1.1.2-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/docutils-0.8.1-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/Jinja2-2.6-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/Pygments-1.4-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/WebHelpers-1.3-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/WebOb-1.2b2-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/xlrd-0.7.1-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/Cython-0.15.1-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/Pyrex-0.9.9-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/virtualenv-1.6.4-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/tornado-2.1.1-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/Twisted-11.0.0-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/biopython-1.58-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/celery-2.4.2-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/pysam-0.5-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/python_dateutil-1.5-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/kombu-1.4.3-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/anyjson-0.3.1-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/DendroPy-3.9.0-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/HTSeq-0.5.3p3-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/networkx-1.5-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/pandas-0.5.0-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/pygr-0.8.2-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/pysparse-1.2_dev-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/rpy2-2.2.4dev_20111114-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/rpy2_bioconductor_extensions-0.2.5_dev-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/scikits.learn-0.8.1-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/scikits.statsmodels-0.3.1-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/scipy-0.10.0-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/sympy-0.7.1-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/CouchDB-0.8-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/h5py-2.0.1-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/MySQL_python-1.2.3-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/pymongo-2.0.1-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/pysqlite-2.6.3-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/psycopg2-2.4.2-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/SQLAlchemy-0.7.3-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/gnuplot_py-1.8-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/PIL-1.1.7-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/pydot-1.0.25-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/pyparsing-1.5.6-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/pygooglechart-0.3.0-py2.7.egg',
 '/usr/local/lib/python2.7/dist-packages/reportlab-2.5-py2.7-linux-x86_64.egg',
 '/usr/local/lib/python2.7/dist-packages/bcbio_nextgen-0.3a-py2.7.egg',
 '/mnt/galaxyData/custom/bin/python_libs',
 '/mnt/galaxyData/custom/MSG_toy',
 '/usr/lib/python2.7',
 '/usr/lib/python2.7/plat-linux2',
 '/usr/lib/python2.7/lib-tk',
 '/usr/lib/python2.7/lib-old',
 '/usr/lib/python2.7/lib-dynload',
 '/usr/local/lib/python2.7/dist-packages',
 '/usr/lib/python2.7/dist-packages',
 '/usr/lib/python2.7/dist-packages/PIL',
 '/usr/lib/python2.7/dist-packages/gst-0.10',
 '/usr/lib/python2.7/dist-packages/gtk-2.0',
 '/usr/lib/pymodules/python2.7',
 '/usr/lib/python2.7/dist-packages/ubuntu-sso-client',
 '/usr/lib/python2.7/dist-packages/wx-2.8-gtk2-unicode']

Answer 1

这样做就可以了：

import os; print(os.path.dirname(__file__))

感谢 @AndiDog 的贡献。

补充：还请注意文档中的提示（这里和 这里）关于 __file__ 的可用性和意义：

一些预定义的（可写的）属性：__name__ 是模块的名称；__doc__ 是模块的文档字符串，如果没有则为 None；__file__ 是加载该模块的文件的路径名，如果是从文件中加载的。对于静态链接到解释器的 C 模块，__file__ 属性是不存在的；对于从共享库动态加载的扩展模块，它是共享库文件的路径名。

__file__ 是由模块加载器提供的名称。如果加载器没有提供文件名信息，这个变量就会被设置为 None。