奇怪的 python sys.path 值

Question

注意sys.path最左边的值，除了空字符串...

从根目录，python -c "import sys; print(sys.path)" 给我：

['', '/home/brian/code/indep/chimai', '/home/brian/code/indep/google_search/src', '/usr/lib/python33.zip', 
'/usr/lib/python3.3', '/usr/lib/python3.3/plat-linux', '/usr/lib/python3.3/lib-dynload', '/usr/lib/python3.3/site-packages']

从我的主目录：

['', '/home/brian/home/brian/code/indep/chimai', '/home/brian/code/indep/google_search/src', 
'/usr/lib/python33.zip', '/usr/lib/python3.3', '/usr/lib/python3.3/plat-linux', '/usr/lib/python3.3/lib-dynload', 
'/usr/lib/python3.3/site-packages']

来自 /boot/grub：

['', '/boot/grub/home/brian/code/indep/chimai', '/home/brian/code/indep/google_search/src', '/usr/lib/python33.zip', 
/usr/lib/python3.3', '/usr/lib/python3.3/plat-linux', '/usr/lib/python3.3/lib-dynload', '/usr/lib/python3.3/site-packages']

无论我从哪个目录进行测试，这种行为都会继续。也就是说，您看到的 sys.path 的第二个和第三个值应该从我的 PYTHONPATH 变量中加载，但第一个值总是将我的当前目录附加到它的前面。

另外，python -Sc "import sys; print(sys.path) 不这样做，出于某种原因。使用该命令，我总是得到：

['', 'home/brian/code/indep/chimai', '/home/brian/code/indep/google_search/src', '/usr/lib/python33.zip', 
'/usr/lib/python3.3/', '/usr/lib/python3.3/plat-linux', '/usr/lib/python3.3/lib-dynload']

这一切都非常令人惊讶。 site.py 对此负责吗？有人可以指出我正确的方向吗？我只是想导入自己的模块，目前由于某种原因无法导入。

Answer 1

来自 site.py 的文档字符串：

"""Append module search paths for third-party packages to sys.path.

****************************************************************
* This module is automatically imported during initialization. *
****************************************************************

In earlier versions of Python (up to 1.5a3), scripts or modules that
needed to use site-specific modules would place ``import site''
somewhere near the top of their code.  Because of the automatic
import, this is no longer necessary (but code that does it still
works).

This will append site-specific paths to the module search path.  On
Unix (including Mac OSX), it starts with sys.prefix and
sys.exec_prefix (if different) and appends
lib/python<version>/site-packages as well as lib/site-python.
On other platforms (such as Windows), it tries each of the
prefixes directly, as well as with lib/site-packages appended.  The
resulting directories, if they exist, are appended to sys.path, and
also inspected for path configuration files.

A path configuration file is a file whose name has the form
<package>.pth; its contents are additional directories (one per line)
to be added to sys.path.  Non-existing directories (or
non-directories) are never added to sys.path; no directory is added to
sys.path more than once.  Blank lines and lines beginning with
'#' are skipped. Lines starting with 'import' are executed.

For example, suppose sys.prefix and sys.exec_prefix are set to
/usr/local and there is a directory /usr/local/lib/python2.5/site-packages
with three subdirectories, foo, bar and spam, and two path
configuration files, foo.pth and bar.pth.  Assume foo.pth contains the
following:

  # foo package configuration
  foo
  bar
  bletch

and bar.pth contains:

  # bar package configuration
  bar

Then the following directories are added to sys.path, in this order:

  /usr/local/lib/python2.5/site-packages/bar
  /usr/local/lib/python2.5/site-packages/foo

Note that bletch is omitted because it doesn't exist; bar precedes foo
because bar.pth comes alphabetically before foo.pth; and spam is
omitted because it is not mentioned in either path configuration file.

After these path manipulations, an attempt is made to import a module
named sitecustomize, which can perform arbitrary additional
site-specific customizations.  If this import fails with an
ImportError exception, it is silently ignored.

"""

就导入您自己的模块而言，以下规则适用：

如果模块在您当前的工作目录中，则可以使用简单的import mymodule 导入，如果它在当前工作目录的子目录中，则可以将其导入为subdir.mymodule，如果您在当前工作目录的子目录和该包包含一个名为__init__.py 的文件，该文件声明了一个名为__all__ = ['modulename', 'another', 'etc'] 的列表，然后您可以from subdir import modulename 或 import subdir 和使用subdir.etc.fn()等

如果您的模块需要在多个地方而不是所有地方使用，您可以将其放在一个公共位置，然后在需要时将该位置附加/插入到 sys.path 中。如果它是您几乎一直都需要的东西，那么您可以将它添加到 your 站点包中，方法是将其放在适当的位置并添加一个 .pth 文件。最后，如果您认为其他人会从您的软件包中受益，您可以使用 distutils 将其捆绑并添加到奶酪店之类的地方或以其他方式分发。