# `sysconfig` --- 提供 Python 設定資訊的存取

在 3.2 版被加入.

原始碼：Lib/sysconfig

The `sysconfig` module provides access to Python's configuration information like the list of installation paths and the configuration variables relevant for the current platform.

## Configuration variables

A Python distribution contains a `Makefile` and a `pyconfig.h` header file that are necessary to build both the Python binary itself and third-party C extensions compiled using `setuptools`.

`sysconfig` puts all variables found in these files in a dictionary that can be accessed using `get_config_vars()` or `get_config_var()`.

Notice that on Windows, it's a much smaller set.

sysconfig.get_config_vars(*args)

  With no arguments, return a dictionary of all configuration variables relevant for the current platform.

  With arguments, return a list of values that result from looking up each argument in the configuration variable dictionary.

  For each argument, if the value is not found, return `None`.

sysconfig.get_config_var(name)

  Return the value of a single variable name. Equivalent to `get_config_vars().get(name)`.

  If name is not found, return `None`.

用法範例：

    >>> import sysconfig
    >>> sysconfig.get_config_var('Py_ENABLE_SHARED')
    0
    >>> sysconfig.get_config_var('LIBDIR')
    '/usr/local/lib'
    >>> sysconfig.get_config_vars('AR', 'CXX')
    ['ar', 'g++']

## Installation paths

Python uses an installation scheme that differs depending on the platform and on the installation options. These schemes are stored in `sysconfig` under unique identifiers based on the value returned by `os.name`. The schemes are used by package installers to determine where to copy files to.

Python currently supports nine schemes:

- posix_prefix: scheme for POSIX platforms like Linux or macOS. This is the default scheme used when Python or a component is installed.

- posix_home: scheme for POSIX platforms, when the home option is used. This scheme defines paths located under a specific home prefix.

- posix_user: scheme for POSIX platforms, when the user option is used. This scheme defines paths located under the user's home directory (`site.USER_BASE`).

- posix_venv: scheme for `Python virtual environments` on POSIX platforms; by default it is the same as posix_prefix.

- nt: scheme for Windows. This is the default scheme used when Python or a component is installed.

- nt_user: scheme for Windows, when the user option is used.

- nt_venv: scheme for `Python virtual environments` on Windows; by default it is the same as nt.

- venv: a scheme with values from either posix_venv or nt_venv depending on the platform Python runs on.

- osx_framework_user: scheme for macOS, when the user option is used.

Each scheme is itself composed of a series of paths and each path has a unique identifier. Python currently uses eight paths:

- stdlib: directory containing the standard Python library files that are not platform-specific.

- platstdlib: directory containing the standard Python library files that are platform-specific.

- platlib: directory for site-specific, platform-specific files.

- purelib: directory for site-specific, non-platform-specific files ('pure' Python).

- include: directory for non-platform-specific header files for the Python C-API.

- platinclude: directory for platform-specific header files for the Python C-API.

- scripts: directory for script files.

- data: directory for data files.

## User scheme

This scheme is designed to be the most convenient solution for users that don't have write permission to the global site-packages directory or don't want to install into it.

Files will be installed into subdirectories of `site.USER_BASE` (written as `userbase` hereafter). This scheme installs pure Python modules and extension modules in the same location (also known as `site.USER_SITE`).

### `posix_user`

Path | Installation directory
--- | ---
stdlib | `userbase/lib/pythonX.Y`
platstdlib | `userbase/lib/pythonX.Y`
platlib | `userbase/lib/pythonX.Y/site-packages`
purelib | `userbase/lib/pythonX.Y/site-packages`
include | `userbase/include/pythonX.Y`
scripts | `userbase/bin`
data | `userbase`

### `nt_user`

Path | Installation directory
--- | ---
stdlib | `userbase\PythonXY`
platstdlib | `userbase\PythonXY`
platlib | `userbase\PythonXY\site-packages`
purelib | `userbase\PythonXY\site-packages`
include | `userbase\PythonXY\Include`
scripts | `userbase\PythonXY\Scripts`
data | `userbase`

### `osx_framework_user`

Path | Installation directory
--- | ---
stdlib | `userbase/lib/python`
platstdlib | `userbase/lib/python`
platlib | `userbase/lib/python/site-packages`
purelib | `userbase/lib/python/site-packages`
include | `userbase/include/pythonX.Y`
scripts | `userbase/bin`
data | `userbase`

## Home scheme

The idea behind the "home scheme" is that you build and maintain a personal stash of Python modules. This scheme's name is derived from the idea of a "home" directory on Unix, since it's not unusual for a Unix user to make their home directory have a layout similar to `/usr/` or `/usr/local/`. This scheme can be used by anyone, regardless of the operating system they are installing for.

### `posix_home`

Path | Installation directory
--- | ---
stdlib | `home/lib/python`
platstdlib | `home/lib/python`
platlib | `home/lib/python`
purelib | `home/lib/python`
include | `home/include/python`
platinclude | `home/include/python`
scripts | `home/bin`
data | `home`

## Prefix scheme

The "prefix scheme" is useful when you wish to use one Python installation to perform the build/install (i.e., to run the setup script), but install modules into the third-party module directory of a different Python installation (or something that looks like a different Python installation). If this sounds a trifle unusual, it is---that's why the user and home schemes come before. However, there are at least two known cases where the prefix scheme will be useful.

First, consider that many Linux distributions put Python in `/usr`, rather than the more traditional `/usr/local`. This is entirely appropriate, since in those cases Python is part of "the system" rather than a local add-on. However, if you are installing Python modules from source, you probably want them to go in `/usr/local/lib/python2.X` rather than `/usr/lib/python2.X`.

Another possibility is a network filesystem where the name used to write to a remote directory is different from the name used to read it: for example, the Python interpreter accessed as `/usr/local/bin/python` might search for modules in `/usr/local/lib/python2.X`, but those modules would have to be installed to, say, `/mnt/@server/export/lib/python2.X`.

### `posix_prefix`

Path | Installation directory
--- | ---
stdlib | `prefix/lib/pythonX.Y`
platstdlib | `prefix/lib/pythonX.Y`
platlib | `prefix/lib/pythonX.Y/site-packages`
purelib | `prefix/lib/pythonX.Y/site-packages`
include | `prefix/include/pythonX.Y`
platinclude | `prefix/include/pythonX.Y`
scripts | `prefix/bin`
data | `prefix`

### `nt`

Path | Installation directory
--- | ---
stdlib | `prefix\Lib`
platstdlib | `prefix\Lib`
platlib | `prefix\Lib\site-packages`
purelib | `prefix\Lib\site-packages`
include | `prefix\Include`
platinclude | `prefix\Include`
scripts | `prefix\Scripts`
data | `prefix`

## 安裝路徑函式

`sysconfig` provides some functions to determine these installation paths.

sysconfig.get_scheme_names()

  Return a tuple containing all schemes currently supported in `sysconfig`.

sysconfig.get_default_scheme()

  Return the default scheme name for the current platform.

  在 3.10 版被加入: This function was previously named `_get_default_scheme()` and considered an implementation detail.

  在 3.11 版的變更: When Python runs from a virtual environment, the venv scheme is returned.

sysconfig.get_preferred_scheme(key)

  Return a preferred scheme name for an installation layout specified by key.

  key must be either `"prefix"`, `"home"`, or `"user"`.

  The return value is a scheme name listed in `get_scheme_names()`. It can be passed to `sysconfig` functions that take a scheme argument, such as `get_paths()`.

  在 3.10 版被加入.

  在 3.11 版的變更: When Python runs from a virtual environment and `key="prefix"`, the venv scheme is returned.

sysconfig._get_preferred_schemes()

  Return a dict containing preferred scheme names on the current platform. Python implementers and redistributors may add their preferred schemes to the `_INSTALL_SCHEMES` module-level global value, and modify this function to return those scheme names, to e.g. provide different schemes for system and language package managers to use, so packages installed by either do not mix with those by the other.

  End users should not use this function, but `get_default_scheme()` and `get_preferred_scheme()` instead.

  在 3.10 版被加入.

sysconfig.get_path_names()

  Return a tuple containing all path names currently supported in `sysconfig`.

sysconfig.get_path(name[, scheme[, vars[, expand]]])

  Return an installation path corresponding to the path name, from the install scheme named scheme.

  name has to be a value from the list returned by `get_path_names()`.

  `sysconfig` stores installation paths corresponding to each path name, for each platform, with variables to be expanded. For instance the stdlib path for the nt scheme is: `{base}/Lib`.

  `get_path()` will use the variables returned by `get_config_vars()` to expand the path. All variables have default values for each platform so one may call this function and get the default value.

  If scheme is provided, it must be a value from the list returned by `get_scheme_names()`. Otherwise, the default scheme for the current platform is used.

  If vars is provided, it must be a dictionary of variables that will update the dictionary returned by `get_config_vars()`.

  If expand is set to `False`, the path will not be expanded using the variables.

  如果找不到 name，則引發 `KeyError`。

sysconfig.get_paths([scheme[, vars[, expand]]])

  Return a dictionary containing all installation paths corresponding to an installation scheme. See `get_path()` for more information.

  If scheme is not provided, will use the default scheme for the current platform.

  If vars is provided, it must be a dictionary of variables that will update the dictionary used to expand the paths.

  If expand is set to false, the paths will not be expanded.

  If scheme is not an existing scheme, `get_paths()` will raise a `KeyError`.

## 其他函式

sysconfig.get_python_version()

  回傳 `MAJOR.MINOR` Python 版本號碼字串。類似於 `'%d.%d' % sys.version_info[:2]`。

sysconfig.get_platform()

  Return a string that identifies the current platform.

  This is used mainly to distinguish platform-specific build directories and platform-specific built distributions. Typically includes the OS name and version and the architecture (as supplied by `os.uname()`), although the exact information included depends on the OS; e.g., on Linux, the kernel version isn't particularly important.

  Examples of returned values:

  - linux-x86_64

  - linux-aarch64

  - solaris-2.6-sun4u

  Windows：

  - win-amd64 (64-bit Windows on AMD64, aka x86_64, Intel64, and EM64T)

  - win-arm64 (64-bit Windows on ARM64, aka AArch64)

  - win32 (all others - specifically, sys.platform is returned)

  POSIX based OS:

  - linux-x86_64

  - macosx-15.5-arm64

  - macosx-26.0-universal2 (macOS on Apple Silicon or Intel)

  - android-24-arm64_v8a

  For other non-POSIX platforms, currently just returns `sys.platform`.

sysconfig.is_python_build()

  Return `True` if the running Python interpreter was built from source and is being run from its built location, and not from a location resulting from e.g. running `make install` or installing via a binary installer.

sysconfig.parse_config_h(fp[, vars])

  剖析一個 `config.h` 風格的檔案。

  fp is a file-like object pointing to the `config.h`-like file.

  A dictionary containing name/value pairs is returned. If an optional dictionary is passed in as the second argument, it is used instead of a new dictionary, and updated with the values read in the file.

sysconfig.get_config_h_filename()

  回傳 `pyconfig.h` 的路徑。

sysconfig.get_makefile_filename()

  回傳 `Makefile` 的路徑。

## 命令列用法

You can use `sysconfig` as a script with Python's -m option:

    $ python -m sysconfig
    Platform: "macosx-10.4-i386"
    Python version: "3.2"
    Current installation scheme: "posix_prefix"

    Paths:
            data = "/usr/local"
            include = "/Users/tarek/Dev/svn.python.org/py3k/Include"
            platinclude = "."
            platlib = "/usr/local/lib/python3.2/site-packages"
            platstdlib = "/usr/local/lib/python3.2"
            purelib = "/usr/local/lib/python3.2/site-packages"
            scripts = "/usr/local/bin"
            stdlib = "/usr/local/lib/python3.2"

    Variables:
            AC_APPLE_UNIVERSAL_BUILD = "0"
            AIX_GENUINE_CPLUSPLUS = "0"
            AR = "ar"
            ARFLAGS = "rc"
            ...

This call will print in the standard output the information returned by `get_platform()`, `get_python_version()`, `get_path()` and `get_config_vars()`.