python：lib/site-packages/site.py 和 lib/site.py 之间的相互作用

Question

由于我设法解决了一个特定的problem，我今天大部分时间都在弄清楚 site.py(s) 是如何工作的。有一点不明白。

据我了解，加载 python 时，首先运行lib/python2.7/site-packages/site.py。它遍历PYTHONPATH，搜索lib/python2.7/site.py，然后导入它。该文件具有addsitedir 方法，不仅添加了sys.path 的路径，还处理了存在于其上的*.pth 文件。此时，lib/python2.7/site.py 中的 main() 运行，addsitedir 在站点包和用户站点包上运行。

现在是奇怪的部分。现在我们回到lib/python2.7/site-packages/site.py，它遍历pythonpath中的每条路径，并在上面运行addsitedir。我觉得这很奇怪，原因有两个：

1. addsitedir 在 lib/python2.7/site-packages 上运行了两次。
2. 这本身并没有那么糟糕（没有什么可以添加到 sys.path 两次），但似乎lib/python2.7/site.py 具有允许雄心勃勃的用户通过实现usercustomize 模块来操纵sys.path 的机制（嘿，它甚至在docs)。显然，当您实施这样的机制时，您希望确保用户最后进入，以便他可以控制添加到sys.path 的所有内容。但这不是这里的情况（因为我很沮丧地发现）。最有可能的是，第二次调用 lib/python2.7/site-packages 将覆盖在 usercustomize 中完成的所有操作。

我知道这很糟糕，但我向addsitedir 添加了一个打印语句，打印它接收到的路径，这样我就可以显示发生了什么。这些是处理的路径：

/home/user/.local/lib/python2.7/site-packages #lib/python2.7/site.py
/home/user/py/lib/python2.7/site-packages     #lib/python2.7/site.py
#This is where your usercustomize runs
#Followin calls are from lib/python2.7/site-packages/site.py
/home/user/py/lib/python2.7/site-packages/numpy-1.9.0-py2.7-linux-x86_64.egg
/home/user/Develop/Python/myproject
/home/user/lmfit-0.7.2
/home/user/py/lib/python2.7/site-packages #NOTE: this runs a second time

那我在这里问什么？ :)

A.对于为什么需要第二次调用 site-packages 的见解，我将不胜感激。

B. usercustomize 是否确实受到限制，因为我认为这是由于这种实现？考虑到这一点，您将如何实现从 sys.path（理论上）删除路径？

---

请求的调试输出：

:genie39:~ ;-) python2.7 -v
# installing zipimport hook
import zipimport # builtin
# installed zipimport hook
# /home/user/py/lib/python2.7/site-packages/site.pyc matches /home/user/py/lib/python2.7/site-packages/site.py
import site # precompiled from /home/user/py/lib/python2.7/site-packages/site.pyc
# /home/user/py/lib/python2.7/os.pyc matches /home/user/py/lib/python2.7/os.py
import os # precompiled from /home/user/py/lib/python2.7/os.pyc
import errno # builtin
import posix # builtin
# /home/user/py/lib/python2.7/posixpath.pyc matches /home/user/py/lib/python2.7/posixpath.py
import posixpath # precompiled from /home/user/py/lib/python2.7/posixpath.pyc
# /home/user/py/lib/python2.7/stat.pyc matches /home/user/py/lib/python2.7/stat.py
import stat # precompiled from /home/user/py/lib/python2.7/stat.pyc
# /home/user/py/lib/python2.7/genericpath.pyc matches /home/user/py/lib/python2.7/genericpath.py
import genericpath # precompiled from /home/user/py/lib/python2.7/genericpath.pyc
# /home/user/py/lib/python2.7/warnings.pyc matches /home/user/py/lib/python2.7/warnings.py
import warnings # precompiled from /home/user/py/lib/python2.7/warnings.pyc
# /home/user/py/lib/python2.7/linecache.pyc matches /home/user/py/lib/python2.7/linecache.py
import linecache # precompiled from /home/user/py/lib/python2.7/linecache.pyc
# /home/user/py/lib/python2.7/types.pyc matches /home/user/py/lib/python2.7/types.py
import types # precompiled from /home/user/py/lib/python2.7/types.pyc
# /home/user/py/lib/python2.7/UserDict.pyc matches /home/user/py/lib/python2.7/UserDict.py
import UserDict # precompiled from /home/user/py/lib/python2.7/UserDict.pyc
# /home/user/py/lib/python2.7/_abcoll.pyc matches /home/user/py/lib/python2.7/_abcoll.py
import _abcoll # precompiled from /home/user/py/lib/python2.7/_abcoll.pyc
# /home/user/py/lib/python2.7/abc.pyc matches /home/user/py/lib/python2.7/abc.py
import abc # precompiled from /home/user/py/lib/python2.7/abc.pyc
# /home/user/py/lib/python2.7/_weakrefset.pyc matches /home/user/py/lib/python2.7/_weakrefset.py
import _weakrefset # precompiled from /home/user/py/lib/python2.7/_weakrefset.pyc
import _weakref # builtin
# /home/user/py/lib/python2.7/copy_reg.pyc matches /home/user/py/lib/python2.7/copy_reg.py
import copy_reg # precompiled from /home/user/py/lib/python2.7/copy_reg.pyc
import imp # builtin
# /home/user/py/lib/python2.7/site.pyc matches /home/user/py/lib/python2.7/site.py
import site # precompiled from /home/user/py/lib/python2.7/site.pyc
# /home/user/py/lib/python2.7/traceback.pyc matches /home/user/py/lib/python2.7/traceback.py
import traceback # precompiled from /home/user/py/lib/python2.7/traceback.pyc
# /home/user/py/lib/python2.7/sysconfig.pyc matches /home/user/py/lib/python2.7/sysconfig.py
import sysconfig # precompiled from /home/user/py/lib/python2.7/sysconfig.pyc
# /home/user/py/lib/python2.7/re.pyc matches /home/user/py/lib/python2.7/re.py
import re # precompiled from /home/user/py/lib/python2.7/re.pyc
# /home/user/py/lib/python2.7/sre_compile.pyc matches /home/user/py/lib/python2.7/sre_compile.py
import sre_compile # precompiled from /home/user/py/lib/python2.7/sre_compile.pyc
import _sre # builtin
# /home/user/py/lib/python2.7/sre_parse.pyc matches /home/user/py/lib/python2.7/sre_parse.py
import sre_parse # precompiled from /home/user/py/lib/python2.7/sre_parse.pyc
# /home/user/py/lib/python2.7/sre_constants.pyc matches /home/user/py/lib/python2.7/sre_constants.py
import sre_constants # precompiled from /home/user/py/lib/python2.7/sre_constants.pyc
# /home/user/py/lib/python2.7/_sysconfigdata.pyc matches /home/user/py/lib/python2.7/_sysconfigdata.py
import _sysconfigdata # precompiled from /home/user/py/lib/python2.7/_sysconfigdata.pyc
# zipimport: found 604 names in /home/user/py/lib/python2.7/site-packages/pytz-2014.7-py2.7.egg
# zipimport: found 20 names in /home/user/py/lib/python2.7/site-packages/hashlib-20081119-py2.7-linux-x86_64.egg
# zipimport: found 40 names in /home/user/py/lib/python2.7/site-packages/pysqlite-2.6.3-py2.7-linux-x86_64.egg
# zipimport: found 7 names in /home/user/py/lib/python2.7/site-packages/mock-1.0.1-py2.7.egg
import encodings # directory /home/user/py/lib/python2.7/encodings
# /home/user/py/lib/python2.7/encodings/__init__.pyc matches /home/user/py/lib/python2.7/encodings/__init__.py
import encodings # precompiled from /home/user/py/lib/python2.7/encodings/__init__.pyc
# /home/user/py/lib/python2.7/codecs.pyc matches /home/user/py/lib/python2.7/codecs.py
import codecs # precompiled from /home/user/py/lib/python2.7/codecs.pyc
import _codecs # builtin
# /home/user/py/lib/python2.7/encodings/aliases.pyc matches /home/user/py/lib/python2.7/encodings/aliases.py
import encodings.aliases # precompiled from /home/user/py/lib/python2.7/encodings/aliases.pyc
# /home/user/py/lib/python2.7/encodings/utf_8.pyc matches /home/user/py/lib/python2.7/encodings/utf_8.py
import encodings.utf_8 # precompiled from /home/user/py/lib/python2.7/encodings/utf_8.pyc
Python 2.7.8 (default, Sep  7 2014, 12:14:33) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
dlopen("/home/user/py/lib/python2.7/site-packages/readline-6.2.4.1-py2.7-linux-x86_64.egg/readline.so", 2);
import readline # dynamically loaded from /home/user/py/lib/python2.7/site-packages/readline-6.2.4.1-py2.7-linux-x86_64.egg/readline.so
>>> 

python -vv 的输出是here

Answer 1

lib/python2.7/site-packages/site.py 文件未正常加载。那是因为lib/python2.7/site.py 的工作是将site-packages 路径添加到sys.path 开头，而site-packages 中的site.py 根本不可见。如果您在site-packages 中有site.py，那么这是一个错误，那里应该没有这样的文件。

没有补丁的 Python 会发生什么：

• Python 以有限的sys.path 启动。 site-packages 不属于此列表，除非您设置了一个包含它的 PYTHONPATH 变量。
• Python 导入site.py，它会导入sys.path 上列出的第一个。
• 找到并加载了lib/python2.7/site.py
• site.py 将 site-packages 添加到 sys.path

就是这样，不再加载site.py 模块。即使您尝试过，它也会找到已经导入的模块； sys.modules['site'] 存在并保存从 lib/python2.7/site.py 加载的对象。

但是，您的安装安装了较旧的setuptools，它包括一个special version of site.py，如果还没有easy_install 命令will install into site-packages。它将通过显式扫描原始sys.path 来加载原始site.py，忽略任何PYTHONPATH 提供的路径，并使用imp.find_module() 和imp.load_module() 低级函数loading the original site.py module manually，从而绕过正常的模块缓存.

它的目的是改变sys.path 的顺序，为PYTHONPATH-listed .pth 文件提供更高的优先级，参见original commit adding the patch：

注意：此版本包含一个被黑的“site.py”以支持处理 .pth 文件位于 sys.path 上 之前 站点包的目录中。

该补丁已从最近的setuptools 版本as early as 2006 in the original setuptools 中完全删除。

因此，您的 Linux 发行版已设置为将 lib/python2.7/site-packages 添加到您的 PYTHONPATH，或者您的 shell 已为您设置此设置，或者您的 Python 已修补以包含它，和 你的site-packages 中有旧的setuptools“补丁”。

删除该文件是完全安全的。