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#459007: merge info from PC/getpathp.c and using/windows.rst to document the forming of sys.path under Windows.

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Georg Brandl 2010-10-17 10:05:13 +00:00
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Doc/using/windows.rst
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@ -156,23 +156,48 @@ installation directory. So, if you had installed Python to
:file:`C:\\Python\\Lib\\` and third-party modules should be stored in
:file:`C:\\Python\\Lib\\site-packages\\`.
.. `` this fixes syntax highlighting errors in some editors due to the \\ hackery
This is how :data:`sys.path` is populated on Windows:
You can add folders to your search path to make Python's import mechanism search
in these directories as well. Use :envvar:`PYTHONPATH`, as described in
:ref:`using-on-envvars`, to modify :data:`sys.path`. On Windows, paths are
separated by semicolons, though, to distinguish them from drive identifiers
(:file:`C:\\` etc.).
* An empty entry is added at the start, which corresponds to the current
directory.
.. ``
* If the environment variable :envvar:`PYTHONPATH` exists, as described in
:ref:`using-on-envvars`, its entries are added next. Note that on Windows,
paths in this variable must be separated by semicolons, to distinguish them
from the colon used in drive identifiers (``C:\`` etc.).
Modifying the module search path can also be done through the Windows registry
under the key :file:`HKLM\\SOFTWARE\\Python\\PythonCore\\{version}\\PythonPath`.
Subkeys which have semicolon-delimited path strings as their default value will
cause each path to be searched. Multiple subkeys can be created and are
appended to the path in alphabetical order. A convenient registry editor is
:program:`regedit` (start it by typing "regedit" into :menuselection:`Start -->
Run`).
* Additional "application paths" can be added in the registry as subkeys of
:samp:`\\SOFTWARE\\Python\\PythonCore\\{version}\\PythonPath` under both the
``HKEY_CURRENT_USER`` and ``HKEY_LOCAL_MACHINE`` hives. Subkeys which have
semicolon-delimited path strings as their default value will cause each path
to be added to :data:`sys.path`. (Note that all known installers only use
HKLM, so HKCU is typically empty.)
* If the environment variable :envvar:`PYTHONHOME` is set, it is assumed as
"Python Home". Otherwise, the path of the main Python executable is used to
locate a "landmark file" (``Lib\os.py``) to deduce the "Python Home". If a
Python home is found, the relevant sub-directories added to :data:`sys.path`
(``Lib``, ``plat-win``, etc) are based on that folder. Otherwise, the core
Python path is constructed from the PythonPath stored in the registry.
* If the Python Home cannot be located, no :envvar:`PYTHONPATH` is specified in
the environment, and no registry entries can be found, a default path with
relative entries is used (e.g. ``.\Lib;.\plat-win``, etc).
The end result of all this is:
* When running :file:`python.exe`, or any other .exe in the main Python
directory (either an installed version, or directly from the PCbuild
directory), the core path is deduced, and the core paths in the registry are
ignored. Other "application paths" in the registry are always read.
* When Python is hosted in another .exe (different directory, embedded via COM,
etc), the "Python Home" will not be deduced, so the core path from the
registry is used. Other "application paths" in the registry are always read.
* If Python can't find its home and there is no registry (eg, frozen .exe, some
very strange installation setup) you get a path with some default, but
relative, paths.
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