Python无法在Ubuntu 14.04上工作（trusty）-无法导入标准库

Question

在服务器上完全卸载python并重新安装python和python-dev之后，python的行为出现了错误。最明显的错误是我无法从标准库中导入许多模块。例如，我无法导入datetime和encodings模块。

[sloria@osf-staging ~]$ python
Python 2.7.6 (default, Mar 22 2014, 22:59:56)
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import datetime
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named datetime
>>> import encodings
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named encodings

这使得无法使用pip、virtualenv等。为什么会发生这种情况？

编辑：这里是dpkg -l | grep python的输出：

[sloria@osf-staging python2.7]$ dpkg -l | grep python
ii  dh-python                            1.20140128-1ubuntu8                 all          Debian helper tools for packaging Python libraries and applications
ii  libpython-dev:amd64                  2.7.5-5ubuntu3                      amd64        header files and a static library for Python (default)
ii  libpython-stdlib:amd64               2.7.5-5ubuntu3                      amd64        interactive high-level object-oriented language (default python version)
ii  libpython2.7:amd64                   2.7.6-8                             amd64        Shared Python runtime library (version 2.7)
ii  libpython2.7-dev:amd64               2.7.6-8                             amd64        Header files and a static library for Python (v2.7)
ii  libpython2.7-minimal:amd64           2.7.6-8                             amd64        Minimal subset of the Python language (version 2.7)
ii  libpython2.7-stdlib:amd64            2.7.6-8                             amd64        Interactive high-level object-oriented language (standard library, version 2.7)
ii  libpython3-stdlib:amd64              3.4.0-0ubuntu2                      amd64        interactive high-level object-oriented language (default python3 version)
rc  libpython3.3-minimal:amd64           3.3.2-7ubuntu3.1                    amd64        Minimal subset of the Python language (version 3.3)
ii  libpython3.4-minimal:amd64           3.4.0-2ubuntu1                      amd64        Minimal subset of the Python language (version 3.4)
ii  libpython3.4-stdlib:amd64            3.4.0-2ubuntu1                      amd64        Interactive high-level object-oriented language (standard library, version 3.4)
ii  python                               2.7.5-5ubuntu3                      amd64        interactive high-level object-oriented language (default version)
ii  python-apt                           0.9.3.5                             amd64        Python interface to libapt-pkg
ii  python-apt-common                    0.9.3.5                             all          Python interface to libapt-pkg (locales)
ii  python-chardet                       2.0.1-2build2                       all          universal character encoding detector
ii  python-colorama                      0.2.5-0.1ubuntu1                    all          Cross-platform colored terminal text in Python - Python 2.x
ii  python-dev                           2.7.5-5ubuntu3                      amd64        header files and a static library for Python (default)
ii  python-distlib                       0.1.8-1                             all          low-level components of python distutils2/packaging
ii  python-html5lib                      0.999-2                             all          HTML parser/tokenizer based on the WHATWG HTML5 specification (Python 2)
ii  python-minimal                       2.7.5-5ubuntu3                      amd64        minimal subset of the Python language (default version)
ii  python-pip                           1.5.4-1                             all          alternative Python package installer
ii  python-pkg-resources                 3.3-1ubuntu1                        all          Package Discovery and Resource Access using pkg_resources
ii  python-requests                      2.2.1-1                             all          elegant and simple HTTP library for Python, built for human beings
ii  python-setuptools                    3.3-1ubuntu1                        all          Python Distutils Enhancements (setuptools compatibility)
ii  python-six                           1.5.2-1                             all          Python 2 and 3 compatibility library (Python 2 interface)
rc  python-support                       1.0.15                              all          automated rebuilding support for Python modules
rc  python-twisted-core                  13.2.0-1ubuntu1                     all          Event-based framework for internet applications
ii  python-urllib3                       1.7.1-1build1                       all          HTTP library with thread-safe connection pooling for Python
ii  python2.7                            2.7.6-8                             amd64        Interactive high-level object-oriented language (version 2.7)
ii  python2.7-dev                        2.7.6-8                             amd64        Header files and a static library for Python (v2.7)
ii  python2.7-minimal                    2.7.6-8                             amd64        Minimal subset of the Python language (version 2.7)
ii  python3                              3.4.0-0ubuntu2                      amd64        interactive high-level object-oriented language (default python3 version)
ii  python3-apparmor                     2.8.95~2430-0ubuntu5                amd64        AppArmor Python3 utility library
ii  python3-dbus                         1.2.0-2build2                       amd64        simple interprocess messaging system (Python 3 interface)
ii  python3-gdbm:amd64                   3.4.0-0ubuntu1                      amd64        GNU dbm database support for Python 3.x
ii  python3-gi                           3.12.0-1                            amd64        Python 3 bindings for gobject-introspection libraries
ii  python3-libapparmor                  2.8.95~2430-0ubuntu5                amd64        AppArmor library Python3 bindings
ii  python3-minimal                      3.4.0-0ubuntu2                      amd64        minimal subset of the Python language (default python3 version)
ii  python3-newt                         0.52.15-2ubuntu5                    amd64        NEWT module for Python3
ii  python3-pkg-resources                3.3-1ubuntu1                        all          Package Discovery and Resource Access using pkg_resources
ii  python3-problem-report               2.14.1-0ubuntu3.2                   all          Python 3 library to handle problem reports
rc  python3.2                            3.2.3-6ubuntu3.5                    amd64        Interactive high-level object-oriented language (version 3.2)
rc  python3.2-minimal                    3.2.3-6ubuntu3.5                    amd64        Minimal subset of the Python language (version 3.2)
rc  python3.3                            3.3.2-7ubuntu3.1                    amd64        Interactive high-level object-oriented language (version 3.3)
rc  python3.3-minimal                    3.3.2-7ubuntu3.1                    amd64        Minimal subset of the Python language (version 3.3)
ii  python3.4                            3.4.0-2ubuntu1                      amd64        Interactive high-level object-oriented language (version 3.4)
ii  python3.4-minimal                    3.4.0-2ubuntu1                      amd64        Minimal subset of the Python language (version 3.4)

Answer 1

我遇到了同样的问题，我通过重新安装python3的stdlib解决了这个问题：

apt-get install --reinstall libpython3.4-stdlib

Answer 2

啊，我想出来了。我在应用程序的虚拟环境中调用chmod -R 770，无意中禁止非根用户访问C标准库文件。事实证明，虚拟环境中的标准库模块不是纯Python（例如datetime模块）符号链接回系统Python的.so文件。因此，更改虚拟环境上的权限也会更改系统Python中相应模块的权限。

因此，我可以通过运行chmod -R 775 /path/to/virtualenv来解决问题。

[掌心]

Answer 3

Ubuntu（和Debian）默认附带两个python包：python和python-minimal。我想发生的事情是你删除了第一个，但由于第二个不依赖于它，你仍然有一个不知何故的工作提示。

顾名思义，这是python的一个非常小的版本，包含的库数量非常有限。您应该能够运行一些简单的脚本，但仅此而已。

python-dev包包含编译扩展所需的文件（从pip安装包时可能需要进一步的文件），但不替换解释器。

要回到正轨，只需重新安装“完整”的python版本：

$ sudo apt-get install python-2.7

这只会将python安装回原来的版本，而不是安装过程中删除的任何已经安装的库。要获取删除内容的列表，可以检查/var/log/apt/history.log的输出。您将看到类似的条目：

Start-Date: 2014-04-21  12:29:19
Commandline: apt-get remove python3.4-dev
Remove: python3.4-dev:amd64 (3.4.0-2ubuntu1), python3-dev:amd64 (3.4.0-0ubuntu2)
End-Date: 2014-04-21  12:29:30

我不知道是什么让你删除了python，但这通常是个坏主意。有些应用程序依赖于显式python版本（以及与之捆绑的库），这在桌面版本中尤其如此。当然，您可以安装其他python版本，只要确保它们不会替换主版本。