Note

The Microsoft Store package is currently considered unstable while its interactions with other tools and other copies of Python are evaluated. While Python itself is stable, this installation method may change its behavior and capabilities during Python 3.7 releases.

Warning

Python will always be available for free on the Microsoft Store. If you are asked to pay for it, you have not selected the correct package.

Note

The embedded distribution does not include the

The two recommended use cases for this distribution are described below.

Python Application

An application written in Python does not necessarily require users to be aware of that fact. The embedded distribution may be used in this case to include a private version of Python in an install package. Depending on how transparent it should be (or conversely, how professional it should appear), there are two options.

Using a specialized executable as a launcher requires some coding, but provides the most transparent experience for users. With a customized launcher, there are no obvious indications that the program is running on Python: icons can be customized, company and version information can be specified, and file associations behave properly. In most cases, a custom launcher should simply be able to call Py_Main with a hard-coded command line.

The simpler approach is to provide a batch file or generated shortcut that directly calls the python.exe or pythonw.exe with the required command-line arguments. In this case, the application will appear to be Python and not its actual name, and users may have trouble distinguishing it from other running Python processes or file associations.

With the latter approach, packages should be installed as directories alongside the Python executable to ensure they are available on the path. With the specialized launcher, packages can be located in other locations as there is an opportunity to specify the search path before launching the application.

Embedding Python

Applications written in native code often require some form of scripting language, and the embedded Python distribution can be used for this purpose. In general, the majority of the application is in native code, and some part will either invoke python.exe or directly use python3.dll. For either case, extracting the embedded distribution to a subdirectory of the application installation is sufficient to provide a loadable Python interpreter.

As with the application use, packages can be installed to any location as there is an opportunity to specify search paths before initializing the interpreter. Otherwise, there is no fundamental differences between using the embedded distribution and a regular installation.

Alternative bundles

Besides the standard CPython distribution, there are modified packages including additional functionality. The following is a list of popular versions and their key features:

Anaconda

Popular scientific modules (such as numpy, scipy and pandas) and the conda package manager.

Configuring Python

To run Python conveniently from a command prompt, you might consider changing some default environment variables in Windows. While the installer provides an option to configure the PATH and PATHEXT variables for you, this is only reliable for a single, system-wide installation. If you regularly use multiple versions of Python, consider using the :ref:`launcher`.

Excursus: Setting environment variables

Windows allows environment variables to be configured permanently at both the User level and the System level, or temporarily in a command prompt.

To temporarily set environment variables, open Command Prompt and use the :command:`set` command:

C:\>set PATH=C:\Program Files\Python 3.7;%PATH%
C:\>set PYTHONPATH=%PYTHONPATH%;C:\My_python_lib
C:\>python

These changes will apply to any further commands executed in that console, and will be inherited by any applications started from the console.

Including the variable name within percent signs will expand to the existing value, allowing you to add your new value at either the start or the end. Modifying :envvar:`PATH` by adding the directory containing :program:`python.exe` to the start is a common way to ensure the correct version of Python is launched.

To permanently modify the default environment variables, click Start and search for 'edit environment variables', or open System properties, :guilabel:`Advanced system settings` and click the :guilabel:`Environment Variables` button. In this dialog, you can add or modify User and System variables. To change System variables, you need non-restricted access to your machine (i.e. Administrator rights).

Note

Windows will concatenate User variables after System variables, which may cause unexpected results when modifying :envvar:`PATH`.

The :envvar:`PYTHONPATH` variable is used by all versions of Python 2 and Python 3, so you should not permanently configure this variable unless it only includes code that is compatible with all of your installed Python versions.

.. seealso::

 https://www.microsoft.com/en-us/wdsi/help/folder-variables
 Environment variables in Windows NT

 https://technet.microsoft.com/en-us/library/cc754250.aspx
 The SET command, for temporarily modifying environment variables

 https://technet.microsoft.com/en-us/library/cc755104.aspx
 The SETX command, for permanently modifying environment variables

 https://support.microsoft.com/en-us/help/310519/how-to-manage-environment-variables-in-windows-xp
 How To Manage Environment Variables in Windows XP

 https://www.chem.gla.ac.uk/~louis/software/faq/q1.html
 Setting Environment variables, Louis J. Farrugia

Finding the Python executable

.. versionchanged:: 3.5

Besides using the automatically created start menu entry for the Python interpreter, you might want to start Python in the command prompt. The installer has an option to set that up for you.

On the first page of the installer, an option labelled "Add Python to PATH" may be selected to have the installer add the install location into the :envvar:`PATH`. The location of the :file:`Scripts\\` folder is also added. This allows you to type :command:`python` to run the interpreter, and :command:`pip` for the package installer. Thus, you can also execute your scripts with command line options, see :ref:`using-on-cmdline` documentation.

If you don't enable this option at install time, you can always re-run the installer, select Modify, and enable it. Alternatively, you can manually modify the :envvar:`PATH` using the directions in :ref:`setting-envvars`. You need to set your :envvar:`PATH` environment variable to include the directory of your Python installation, delimited by a semicolon from other entries. An example variable could look like this (assuming the first two entries already existed):

C:\WINDOWS\system32;C:\WINDOWS;C:\Program Files\Python 3.7

Python Launcher for Windows

.. versionadded:: 3.3

The Python launcher for Windows is a utility which aids in locating and executing of different Python versions. It allows scripts (or the command-line) to indicate a preference for a specific Python version, and will locate and execute that version.

Unlike the :envvar:`PATH` variable, the launcher will correctly select the most appropriate version of Python. It will prefer per-user installations over system-wide ones, and orders by language version rather than using the most recently installed version.

The launcher was originally specified in Getting started

From the command-line

.. versionchanged:: 3.6

System-wide installations of Python 3.3 and later will put the launcher on your :envvar:`PATH`. The launcher is compatible with all available versions of Python, so it does not matter which version is installed. To check that the launcher is available, execute the following command in Command Prompt:

py

You should find that the latest version of Python you have installed is started - it can be exited as normal, and any additional command-line arguments specified will be sent directly to Python.

If you have multiple versions of Python installed (e.g., 2.7 and |version|) you will have noticed that Python |version| was started - to launch Python 2.7, try the command:

py -2.7

If you want the latest version of Python 2.x you have installed, try the command:

py -2

You should find the latest version of Python 2.x starts.

If you see the following error, you do not have the launcher installed:

'py' is not recognized as an internal or external command,
operable program or batch file.

Per-user installations of Python do not add the launcher to :envvar:`PATH` unless the option was selected on installation.

Virtual environments

.. versionadded:: 3.5

If the launcher is run with no explicit Python version specification, and a virtual environment (created with the standard library :mod:`venv` module or the external virtualenv tool) active, the launcher will run the virtual environment's interpreter rather than the global one. To run the global interpreter, either deactivate the virtual environment, or explicitly specify the global Python version.

From a script

Let's create a test Python script - create a file called hello.py with the following contents

#! python
import sys
sys.stdout.write("hello from Python %s\n" % (sys.version,))

From the directory in which hello.py lives, execute the command:

py hello.py

You should notice the version number of your latest Python 2.x installation is printed. Now try changing the first line to be:

#! python3

Re-executing the command should now print the latest Python 3.x information. As with the above command-line examples, you can specify a more explicit version qualifier. Assuming you have Python 2.6 installed, try changing the first line to #! python2.6 and you should find the 2.6 version information printed.

Note that unlike interactive use, a bare "python" will use the latest version of Python 2.x that you have installed. This is for backward compatibility and for compatibility with Unix, where the command python typically refers to Python 2.

From file associations

The launcher should have been associated with Python files (i.e. .py, .pyw, .pyc files) when it was installed. This means that when you double-click on one of these files from Windows explorer the launcher will be used, and therefore you can use the same facilities described above to have the script specify the version which should be used.

The key benefit of this is that a single launcher can support multiple Python versions at the same time depending on the contents of the first line.

Shebang Lines

If the first line of a script file starts with #!, it is known as a "shebang" line. Linux and other Unix like operating systems have native support for such lines and they are commonly used on such systems to indicate how a script should be executed. This launcher allows the same facilities to be used with Python scripts on Windows and the examples above demonstrate their use.

To allow shebang lines in Python scripts to be portable between Unix and Windows, this launcher supports a number of 'virtual' commands to specify which interpreter to use. The supported virtual commands are:

• /usr/bin/env python
• /usr/bin/python
• /usr/local/bin/python
• python

For example, if the first line of your script starts with

#! /usr/bin/python

The default Python will be located and used. As many Python scripts written to work on Unix will already have this line, you should find these scripts can be used by the launcher without modification. If you are writing a new script on Windows which you hope will be useful on Unix, you should use one of the shebang lines starting with /usr.

Any of the above virtual commands can be suffixed with an explicit version (either just the major version, or the major and minor version). Furthermore the 32-bit version can be requested by adding "-32" after the minor version. I.e. /usr/bin/python2.7-32 will request usage of the 32-bit python 2.7.

.. versionadded:: 3.7

 Beginning with python launcher 3.7 it is possible to request 64-bit version
 by the "-64" suffix. Furthermore it is possible to specify a major and
 architecture without minor (i.e. ``/usr/bin/python3-64``).

The /usr/bin/env form of shebang line has one further special property. Before looking for installed Python interpreters, this form will search the executable :envvar:`PATH` for a Python executable. This corresponds to the behaviour of the Unix env program, which performs a :envvar:`PATH` search.

Arguments in shebang lines

The shebang lines can also specify additional options to be passed to the Python interpreter. For example, if you have a shebang line:

#! /usr/bin/python -v

Then Python will be started with the -v option

Customization

Customization via INI files

Two .ini files will be searched by the launcher - py.ini in the current user's "application data" directory (i.e. the directory returned by calling the Windows function SHGetFolderPath with CSIDL_LOCAL_APPDATA) and py.ini in the same directory as the launcher. The same .ini files are used for both the 'console' version of the launcher (i.e. py.exe) and for the 'windows' version (i.e. pyw.exe).

Customization specified in the "application directory" will have precedence over the one next to the executable, so a user, who may not have write access to the .ini file next to the launcher, can override commands in that global .ini file.

Customizing default Python versions

In some cases, a version qualifier can be included in a command to dictate which version of Python will be used by the command. A version qualifier starts with a major version number and can optionally be followed by a period ('.') and a minor version specifier. Furthermore it is possible to specifiy if a 32 or 64 bit implementation shall be requested by adding "-32" or "-64".

For example, a shebang line of #!python has no version qualifier, while #!python3 has a version qualifier which specifies only a major version.

If no version qualifiers are found in a command, the environment variable :envvar:`PY_PYTHON` can be set to specify the default version qualifier. If it is not set, the default is "3". The variable can specify any value that may be passed on the command line, such as "3", "3.7", "3.7-32" or "3.7-64". (Note that the "-64" option is only available with the launcher included with Python 3.7 or newer.)

If no minor version qualifiers are found, the environment variable PY_PYTHON{major} (where {major} is the current major version qualifier as determined above) can be set to specify the full version. If no such option is found, the launcher will enumerate the installed Python versions and use the latest minor release found for the major version, which is likely, although not guaranteed, to be the most recently installed version in that family.

On 64-bit Windows with both 32-bit and 64-bit implementations of the same (major.minor) Python version installed, the 64-bit version will always be preferred. This will be true for both 32-bit and 64-bit implementations of the launcher - a 32-bit launcher will prefer to execute a 64-bit Python installation of the specified version if available. This is so the behavior of the launcher can be predicted knowing only what versions are installed on the PC and without regard to the order in which they were installed (i.e., without knowing whether a 32 or 64-bit version of Python and corresponding launcher was installed last). As noted above, an optional "-32" or "-64" suffix can be used on a version specifier to change this behaviour.

Examples:

• If no relevant options are set, the commands python and python2 will use the latest Python 2.x version installed and the command python3 will use the latest Python 3.x installed.
• The commands python3.1 and python2.7 will not consult any options at all as the versions are fully specified.
• If PY_PYTHON=3, the commands python and python3 will both use the latest installed Python 3 version.
• If PY_PYTHON=3.1-32, the command python will use the 32-bit implementation of 3.1 whereas the command python3 will use the latest installed Python (PY_PYTHON was not considered at all as a major version was specified.)
• If PY_PYTHON=3 and PY_PYTHON3=3.1, the commands python and python3 will both use specifically 3.1

In addition to environment variables, the same settings can be configured in the .INI file used by the launcher. The section in the INI file is called [defaults] and the key name will be the same as the environment variables without the leading PY_ prefix (and note that the key names in the INI file are case insensitive.) The contents of an environment variable will override things specified in the INI file.

For example:

• Setting PY_PYTHON=3.1 is equivalent to the INI file containing:

[defaults]
python=3.1

• Setting PY_PYTHON=3 and PY_PYTHON3=3.1 is equivalent to the INI file containing:

[defaults]
python=3
python3=3.1

Diagnostics

If an environment variable PYLAUNCH_DEBUG is set (to any value), the launcher will print diagnostic information to stderr (i.e. to the console). While this information manages to be simultaneously verbose and terse, it should allow you to see what versions of Python were located, why a particular version was chosen and the exact command-line used to execute the target Python.

Finding modules

Python usually stores its library (and thereby your site-packages folder) in the installation directory. So, if you had installed Python to :file:`C:\\Python\\`, the default library would reside in :file:`C:\\Python\\Lib\\` and third-party modules should be stored in :file:`C:\\Python\\Lib\\site-packages\\`.

To completely override :data:`sys.path`, create a ._pth file with the same name as the DLL (python37._pth) or the executable (python._pth) and specify one line for each path to add to :data:`sys.path`. The file based on the DLL name overrides the one based on the executable, which allows paths to be restricted for any program loading the runtime if desired.

When the file exists, all registry and environment variables are ignored, isolated mode is enabled, and :mod:`site` is not imported unless one line in the file specifies import site. Blank paths and lines starting with # are ignored. Each path may be absolute or relative to the location of the file. Import statements other than to site are not permitted, and arbitrary code cannot be specified.

Note that .pth files (without leading underscore) will be processed normally by the :mod:`site` module when import site has been specified.

When no ._pth file is found, this is how :data:`sys.path` is populated on Windows:

• 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.).
• 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" (either Lib\os.py or pythonXY.zip) 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).

If a pyvenv.cfg file is found alongside the main executable or in the directory one level above the executable, the following variations apply:

• If home is an absolute path and :envvar:`PYTHONHOME` is not set, this path is used instead of the path to the main executable when deducing the home location.

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 are no registry value (frozen .exe, some very strange installation setup) you get a path with some default, but relative, paths.

For those who want to bundle Python into their application or distribution, the following advice will prevent conflicts with other installations:

• Include a ._pth file alongside your executable containing the directories to include. This will ignore paths listed in the registry and environment variables, and also ignore :mod:`site` unless import site is listed.
• If you are loading :file:`python3.dll` or :file:`python37.dll` in your own executable, explicitly call :c:func:`Py_SetPath` or (at least) :c:func:`Py_SetProgramName` before :c:func:`Py_Initialize`.
• Clear and/or overwrite :envvar:`PYTHONPATH` and set :envvar:`PYTHONHOME` before launching :file:`python.exe` from your application.
• If you cannot use the previous suggestions (for example, you are a distribution that allows people to run :file:`python.exe` directly), ensure that the landmark file (:file:`Lib\\os.py`) exists in your install directory. (Note that it will not be detected inside a ZIP file, but a correctly named ZIP file will be detected instead.)

These will ensure that the files in a system-wide installation will not take precedence over the copy of the standard library bundled with your application. Otherwise, your users may experience problems using your application. Note that the first suggestion is the best, as the others may still be susceptible to non-standard paths in the registry and user site-packages.

.. versionchanged::
 3.6

 * Adds ``._pth`` file support and removes ``applocal`` option from
 ``pyvenv.cfg``.
 * Adds ``pythonXX.zip`` as a potential landmark when directly adjacent
 to the executable.

.. deprecated::
 3.6

 Modules specified in the registry under ``Modules`` (not ``PythonPath``)
 may be imported by :class:`importlib.machinery.WindowsRegistryFinder`.
 This finder is enabled on Windows in 3.6.0 and earlier, but may need to
 be explicitly added to :attr:`sys.meta_path` in the future.

Additional modules

Even though Python aims to be portable among all platforms, there are features that are unique to Windows. A couple of modules, both in the standard library and external, and snippets exist to use these features.

The Windows-specific standard modules are documented in :ref:`mswin-specific-services`.

PyWin32

The Component Object Model (COM)

Win32 API calls

Registry

Event log

PythonWin is a sample MFC application shipped with PyWin32. It is an embeddable IDE with a built-in debugger.

.. seealso::

 `Win32 How Do I...? <http://timgolden.me.uk/python/win32_how_do_i.html>`_
 by Tim Golden

 `Python and COM <http://www.boddie.org.uk/python/COM.html>`_
 by David and Paul Boddie

cx_Freeze

:mod:`distutils` extension (see :ref:`extending-distutils`) which wraps Python scripts into executable Windows programs (:file:`{*}.exe` files). When you have done this, you can distribute your application without requiring your users to install Python.

WConio

Since Python's advanced terminal handling layer, :mod:`curses`, is restricted to Unix-like systems, there is a library exclusive to Windows as well: Windows Console I/O for Python.

:file:`CONIO.H`, used to create text user interfaces.

Compiling Python on Windows

If you want to compile CPython yourself, first thing you should do is get the checkout.

The source tree contains a build solution and project files for Microsoft Visual Studio 2015, which is the compiler used to build the official Python releases. These files are in the :file:`PCbuild` directory.

Check :file:`PCbuild/readme.txt` for general information on the build process.

For extension modules, consult :ref:`building-on-windows`.

.. seealso::

 `Python + Windows + distutils + SWIG + gcc MinGW <http://sebsauvage.net/python/mingw.html>`_
 or "Creating Python extensions in C/C++ with SWIG and compiling them with
 MinGW gcc under Windows" or "Installing Python extension with distutils
 and without Microsoft Visual C++" by Sébastien Sauvage, 2003

 `MingW -- Python extensions <http://www.mingw.org/wiki/FAQ#toc14>`_

Other Platforms

With ongoing development of Python, some platforms that used to be supported earlier are no longer supported (due to the lack of users or developers). Check Windows CE is still supported.

The Maintainer releases)

See /python_sourcecode/python3.7.4/blob/master/Doc/using/windows.rst