Where Is Python Installed Windows

4. Using Python on Windows¶

This certificate aims to give an overview of Windows-specific behaviour you should know about when using Python on Microsoft Windows.

Dissimilar most Unix systems and services, Windows does non include a arrangement supported installation of Python. To make Python bachelor, the CPython team has compiled Windows installers (MSI packages) with every release for many years. These installers are primarily intended to add a per-user installation of Python, with the cadre interpreter and library beingness used by a single user. The installer is besides able to install for all users of a single machine, and a separate ZIP file is available for application-local distributions.

As specified in PEP 11, a Python release only supports a Windows platform while Microsoft considers the platform under extended support. This ways that Python 3.10 supports Windows 8.1 and newer. If y'all crave Windows vii support, please install Python 3.8.

There are a number of unlike installers bachelor for Windows, each with certain benefits and downsides.

The full installer contains all components and is the best selection for developers using Python for whatever kind of projection.

The Microsoft Shop package is a simple installation of Python that is suitable for running scripts and packages, and using IDLE or other development environments. It requires Windows ten, simply can be safely installed without corrupting other programs. It also provides many user-friendly commands for launching Python and its tools.

The nuget.org packages are lightweight installations intended for continuous integration systems. It can exist used to build Python packages or run scripts, simply is not updateable and has no user interface tools.

The embeddable package is a minimal package of Python suitable for embedding into a larger application.

4.one. The full installer¶

4.one.1. Installation steps¶

Four Python 3.10 installers are available for download - 2 each for the 32-bit and 64-bit versions of the interpreter. The web installer is a small initial download, and information technology will automatically download the required components as necessary. The offline installer includes the components necessary for a default installation and only requires an internet connection for optional features. See Installing Without Downloading for other ways to avoid downloading during installation.

After starting the installer, 1 of two options may be selected:

If y'all select "Install Now":

You will not demand to be an administrator (unless a system update for the C Runtime Library is required or you install the Python Launcher for Windows for all users)
Python will be installed into your user directory
The Python Launcher for Windows volition exist installed according to the option at the bottom of the first page
The standard library, test suite, launcher and pip will be installed
If selected, the install directory volition exist added to your PATH
Shortcuts will merely be visible for the electric current user

Selecting "Customize installation" will allow yous to select the features to install, the installation location and other options or mail-install actions. To install debugging symbols or binaries, you volition need to utilize this selection.

To perform an all-users installation, you should select "Customize installation". In this case:

You may be required to provide authoritative credentials or approval
Python will be installed into the Program Files directory
The Python Launcher for Windows will be installed into the Windows directory
Optional features may be selected during installation
The standard library tin exist pre-compiled to bytecode
If selected, the install directory will be added to the system PATH
Shortcuts are available for all users

4.one.ii. Removing the MAX_PATH Limitation¶

Windows historically has limited path lengths to 260 characters. This meant that paths longer than this would not resolve and errors would result.

In the latest versions of Windows, this limitation tin can be expanded to approximately 32,000 characters. Your administrator will demand to activate the "Enable Win32 long paths" group policy, or set LongPathsEnabled to ane in the registry key HKEY_LOCAL_MACHINE\Arrangement\CurrentControlSet\Control\FileSystem .

This allows the open() function, the os module and near other path functionality to take and return paths longer than 260 characters.

Afterwards changing the above option, no further configuration is required.

Inverse in version iii.6: Support for long paths was enabled in Python.

4.i.3. Installing Without UI¶

All of the options available in the installer UI tin also be specified from the command line, assuasive scripted installers to replicate an installation on many machines without user interaction. These options may also be set without suppressing the UI in lodge to change some of the defaults.

To completely hide the installer UI and install Python silently, laissez passer the /placidity option. To skip past the user interaction but still display progress and errors, laissez passer the /passive option. The /uninstall pick may be passed to immediately begin removing Python - no confirmation prompt volition be displayed.

All other options are passed as name=value , where the value is normally 0 to disable a characteristic, 1 to enable a feature, or a path. The total list of available options is shown below.

Name	Clarification	Default
InstallAllUsers	Perform a organisation-wide installation.	0
TargetDir	The installation directory	Selected based on InstallAllUsers
DefaultAllUsersTargetDir	The default installation directory for all-user installs	`%ProgramFiles%\Python X.Y` or `%ProgramFiles(x86)%\Python Ten.Y`
DefaultJustForMeTargetDir	The default install directory for simply-for-me installs	`%LocalAppData%\Programs\PythonXY` or `%LocalAppData%\Programs\PythonXY-32` or `%LocalAppData%\Programs\PythonXY-64`
DefaultCustomTargetDir	The default custom install directory displayed in the UI	(empty)
AssociateFiles	Create file associations if the launcher is also installed.	1
CompileAll	Compile all `.py` files to `.pyc` .	0
PrependPath	Add install and Scripts directories to `PATH` and `.PY` to `PATHEXT`	0
Shortcuts	Create shortcuts for the interpreter, documentation and IDLE if installed.	1
Include_doc	Install Python manual	i
Include_debug	Install debug binaries	0
Include_dev	Install developer headers and libraries	one
Include_exe	Install `python.exe` and related files	1
Include_launcher	Install Python Launcher for Windows.	1
InstallLauncherAllUsers	Installs Python Launcher for Windows for all users.	1
Include_lib	Install standard library and extension modules	1
Include_pip	Install bundled pip and setuptools	1
Include_symbols	Install debugging symbols (*.pdb)	0
Include_tcltk	Install Tcl/Tk support and IDLE	1
Include_test	Install standard library test suite	1
Include_tools	Install utility scripts	1
LauncherOnly	Only installs the launcher. This will override near other options.	0
SimpleInstall	Disable about install UI	0
SimpleInstallDescription	A custom message to brandish when the simplified install UI is used.	(empty)

For example, to silently install a default, organisation-wide Python installation, you could use the following command (from an elevated command prompt):

                python-iii.ix.0.exe /tranquility InstallAllUsers=ane PrependPath=1 Include_test=0

To allow users to easily install a personal copy of Python without the test suite, you could provide a shortcut with the following command. This will display a simplified initial folio and disallow customization:

                python-three.nine.0.exe InstallAllUsers=0 Include_launcher=0 Include_test=0     SimpleInstall=1 SimpleInstallDescription="Just for me, no test suite."

(Note that omitting the launcher besides omits file associations, and is but recommended for per-user installs when in that location is besides a system-broad installation that included the launcher.)

The options listed above can too be provided in a file named unattend.xml alongside the executable. This file specifies a list of options and values. When a value is provided as an attribute, information technology volition be converted to a number if possible. Values provided every bit chemical element text are always left as strings. This example file sets the same options as the previous example:

                                <Options>                <Choice                Name=                "InstallAllUsers"                Value=                "no"                />                <Choice                Name=                "Include_launcher"                Value=                "0"                />                <Option                Proper noun=                "Include_test"                Value=                "no"                />                <Choice                Name=                "SimpleInstall"                Value=                "yep"                />                <Option                Proper name=                "SimpleInstallDescription"                >Merely for me, no test suite</Option>                </Options>

4.1.four. Installing Without Downloading¶

As some features of Python are non included in the initial installer download, selecting those features may require an cyberspace connectedness. To avoid this demand, all possible components may be downloaded on-demand to create a consummate layout that will no longer crave an internet connection regardless of the selected features. Note that this download may be bigger than required, but where a big number of installations are going to exist performed information technology is very useful to take a locally cached re-create.

Execute the post-obit control from Command Prompt to download all possible required files. Remember to substitute python-3.nine.0.exe for the actual proper name of your installer, and to create layouts in their own directories to avoid collisions betwixt files with the same proper name.

                python-3.9.0.exe /layout [optional target directory]

Yous may likewise specify the /quiet option to hide the progress brandish.

iv.1.5. Modifying an install¶

One time Python has been installed, you tin can add or remove features through the Programs and Features tool that is part of Windows. Select the Python entry and choose "Uninstall/Change" to open the installer in maintenance mode.

"Modify" allows yous to add or remove features by modifying the checkboxes - unchanged checkboxes will not install or remove annihilation. Some options cannot exist changed in this mode, such as the install directory; to modify these, you will demand to remove and then reinstall Python completely.

"Repair" volition verify all the files that should be installed using the electric current settings and supplant any that have been removed or modified.

"Uninstall" volition remove Python entirely, with the exception of the Python Launcher for Windows, which has its ain entry in Programs and Features.

4.ii. The Microsoft Store package¶

New in version 3.7.2.

The Microsoft Shop package is an easily installable Python interpreter that is intended mainly for interactive apply, for example, by students.

To install the package, ensure you accept the latest Windows ten updates and search the Microsoft Store app for "Python 3.10". Ensure that the app you select is published past the Python Software Foundation, and install information technology.

Alert

Python volition e'er be bachelor for gratuitous on the Microsoft Store. If you are asked to pay for it, you have non selected the right package.

After installation, Python may exist launched by finding it in Showtime. Alternatively, information technology will be available from whatever Control Prompt or PowerShell session past typing python . Further, pip and IDLE may exist used by typing pip or idle . IDLE tin also be plant in Get-go.

All iii commands are also available with version number suffixes, for example, as python3.exe and python3.ten.exe too as python.exe (where 3.x is the specific version y'all desire to launch, such as 3.10). Open "Manage App Execution Aliases" through Start to select which version of Python is associated with each command. It is recommended to brand sure that pip and idle are consistent with whichever version of python is selected.

Virtual environments can be created with python -thousand venv and activated and used equally normal.

If you have installed some other version of Python and added it to your PATH variable, it will be available as python.exe rather than the one from the Microsoft Store. To access the new installation, utilize python3.exe or python3.x.exe .

The py.exe launcher will detect this Python installation, but will adopt installations from the traditional installer.

To remove Python, open Settings and use Apps and Features, or else find Python in Start and correct-click to select Uninstall. Uninstalling will remove all packages you installed directly into this Python installation, but will not remove any virtual environments

4.2.1. Known Bug¶

Because of restrictions on Microsoft Store apps, Python scripts may non have full write access to shared locations such as TEMP and the registry. Instead, it will write to a private copy. If your scripts must modify the shared locations, you will need to install the full installer.

For more than detail on the technical footing for these limitations, please consult Microsoft's documentation on packaged total-trust apps, currently available at docs.microsoft.com/en-us/windows/msix/desktop/desktop-to-uwp-behind-the-scenes

4.3. The nuget.org packages¶

New in version three.5.2.

The nuget.org parcel is a reduced size Python environs intended for employ on continuous integration and build systems that practise not have a system-wide install of Python. While nuget is "the package manager for .Net", it also works perfectly fine for packages containing build-time tools.

Visit nuget.org for the virtually up-to-engagement information on using nuget. What follows is a summary that is sufficient for Python developers.

The nuget.exe command line tool may exist downloaded directly from https://aka.ms/nugetclidl , for example, using curl or PowerShell. With the tool, the latest version of Python for 64-bit or 32-bit machines is installed using:

              nuget.exe install python -ExcludeVersion -OutputDirectory . nuget.exe install pythonx86 -ExcludeVersion -OutputDirectory .

To select a particular version, add a -Version three.ten.y . The output directory may be changed from . , and the package will be installed into a subdirectory. By default, the subdirectory is named the aforementioned equally the packet, and without the -ExcludeVersion option this proper name will include the specific version installed. Inside the subdirectory is a tools directory that contains the Python installation:

              # Without -ExcludeVersion > .\python.3.5.2\tools\python.exe -5 Python 3.5.ii  # With -ExcludeVersion > .\python\tools\python.exe -V Python iii.5.2

In full general, nuget packages are non upgradeable, and newer versions should exist installed side-by-side and referenced using the full path. Alternatively, delete the parcel directory manually and install it over again. Many CI systems will do this automatically if they practise not preserve files between builds.

Alongside the tools directory is a build\native directory. This contains a MSBuild backdrop file python.props that tin exist used in a C++ project to reference the Python install. Including the settings will automatically use the headers and import libraries in your build.

The packet information pages on nuget.org are www.nuget.org/packages/python for the 64-bit version and www.nuget.org/packages/pythonx86 for the 32-fleck version.

4.four. The embeddable packet¶

New in version 3.5.

The embedded distribution is a Zilch file containing a minimal Python environment. It is intended for acting equally part of another application, rather than being directly accessed by end-users.

When extracted, the embedded distribution is (almost) fully isolated from the user'due south organisation, including environment variables, system registry settings, and installed packages. The standard library is included every bit pre-compiled and optimized .pyc files in a ZIP, and python3.dll , python37.dll , python.exe and pythonw.exe are all provided. Tcl/tk (including all dependants, such as Idle), pip and the Python documentation are not included.

Annotation

The embedded distribution does not include the Microsoft C Runtime and it is the responsibility of the awarding installer to provide this. The runtime may accept already been installed on a user's system previously or automatically via Windows Update, and can be detected by finding ucrtbase.dll in the system directory.

Third-party packages should be installed past the application installer alongside the embedded distribution. Using pip to manage dependencies as for a regular Python installation is not supported with this distribution, though with some intendance it may be possible to include and use pip for automatic updates. In general, third-political party packages should exist treated as part of the application ("vendoring") so that the developer can ensure compatibility with newer versions before providing updates to users.

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

4.4.1. Python Application¶

An application written in Python does not necessarily crave users to exist aware of that fact. The embedded distribution may be used in this case to include a private version of Python in an install packet. Depending on how transparent it should be (or conversely, how professional information technology should appear), at that place 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 tin exist customized, visitor and version information can exist 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 bodily proper name, and users may have trouble distinguishing it from other running Python processes or file associations.

With the latter arroyo, packages should exist installed as directories alongside the Python executable to ensure they are available on the path. With the specialized launcher, packages can exist located in other locations equally at that place is an opportunity to specify the search path before launching the awarding.

4.iv.2. Embedding Python¶

Applications written in native code oft crave some form of scripting language, and the embedded Python distribution can be used for this purpose. In full 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 whatsoever location as in that location is an opportunity to specify search paths earlier initializing the interpreter. Otherwise, in that location is no cardinal differences between using the embedded distribution and a regular installation.

4.five. Culling bundles¶

Besides the standard CPython distribution, in that location are modified packages including additional functionality. The following is a list of pop versions and their fundamental features:

ActivePython: Installer with multi-platform compatibility, documentation, PyWin32
Anaconda: Popular scientific modules (such equally numpy, scipy and pandas) and the conda package manager.
Canopy: A "comprehensive Python analysis environment" with editors and other development tools.
WinPython: Windows-specific distribution with prebuilt scientific packages and tools for edifice packages.

Notation that these packages may not include the latest versions of Python or other libraries, and are not maintained or supported past the cadre Python team.

4.vi. 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 merely reliable for a single, organisation-broad installation. If you regularly use multiple versions of Python, consider using the Python Launcher for Windows.

four.6.1. 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 control prompt.

To temporarily ready surroundings variables, open Control Prompt and use the fix command:

                                C:\>                prepare                PATH                =C:\Program Files\Python iii.9;%PATH%                C:\>                set                PYTHONPATH                =                %PYTHONPATH%;C:\My_python_lib                C:\>python

These changes volition apply to any further commands executed in that console, and volition exist inherited past any applications started from the console.

Including the variable proper name within percent signs will expand to the existing value, assuasive y'all to add your new value at either the start or the end. Modifying PATH past adding the directory containing python.exe to the start is a mutual way to ensure the correct version of Python is launched.

To permanently modify the default environment variables, click Outset and search for 'edit surroundings variables', or open System properties, Avant-garde organization settings and click the Environs Variables button. In this dialog, you can add or change User and Arrangement variables. To modify System variables, you lot need non-restricted access to your machine (i.e. Administrator rights).

Notation

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

The PYTHONPATH variable is used by all versions of Python 2 and Python 3, then you lot should not permanently configure this variable unless it but includes code that is compatible with all of your installed Python versions.

iv.vi.2. Finding the Python executable¶

Inverse in version 3.five.

Besides using the automatically created start bill of fare entry for the Python interpreter, yous might want to showtime Python in the command prompt. The installer has an option to set that upwards for yous.

On the first page of the installer, an option labelled "Add Python to PATH" may be selected to take the installer add the install location into the PATH . The location of the Scripts\ folder is also added. This allows you to blazon python to run the interpreter, and pip for the package installer. Thus, you can likewise execute your scripts with command line options, run into Command line documentation.

If you don't enable this pick at install time, you tin always re-run the installer, select Modify, and enable it. Alternatively, you tin can manually modify the PATH using the directions in Excursus: Setting environment variables. You need to set your PATH surround 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 offset two entries already existed):

                C:\WINDOWS\system32;C:\WINDOWS;C:\Program Files\Python three.9

4.seven. UTF-8 way¶

New in version 3.7.

Windows notwithstanding uses legacy encodings for the system encoding (the ANSI Lawmaking Folio). Python uses it for the default encoding of text files (due east.g. locale.getpreferredencoding() ).

This may cause issues because UTF-8 is widely used on the internet and most Unix systems, including WSL (Windows Subsystem for Linux).

You can apply the Python UTF-viii Mode to change the default text encoding to UTF-8. You can enable the Python UTF-eight Mode via the -X utf8 command line option, or the PYTHONUTF8=1 surroundings variable. Run into PYTHONUTF8 for enabling UTF-eight way, and Excursus: Setting environment variables for how to modify surroundings variables.

When the Python UTF-8 Mode is enabled, you can yet use the organisation encoding (the ANSI Code Page) via the "mbcs" codec.

Note that calculation PYTHONUTF8=1 to the default environment variables will affect all Python iii.seven+ applications on your system. If you have whatsoever Python 3.vii+ applications which rely on the legacy system encoding, it is recommended to ready the environment variable temporarily or utilize the -Ten utf8 command line option.

Notation

Even when UTF-eight mode is disabled, Python uses UTF-8 by default on Windows for:

Console I/O including standard I/O (encounter PEP 528 for details).
The filesystem encoding (see PEP 529 for details).

4.8. Python Launcher for Windows¶

New in version 3.3.

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

Unlike the PATH variable, the launcher volition correctly select the most advisable version of Python. It will prefer per-user installations over system-wide ones, and orders past language version rather than using the almost recently installed version.

The launcher was originally specified in PEP 397.

4.8.1. Getting started¶

4.8.1.i. From the control-line¶

Changed in version 3.six.

System-wide installations of Python 3.three and later will put the launcher on your PATH . The launcher is uniform with all bachelor versions of Python, and so it does non affair which version is installed. To check that the launcher is available, execute the following command in Command Prompt:

You should find that the latest version of Python you lot take installed is started - information technology tin be exited as normal, and any additional command-line arguments specified will be sent straight to Python.

If you have multiple versions of Python installed (due east.yard., 2.vii and 3.x) y'all volition have noticed that Python 3.x was started - to launch Python 2.vii, attempt the command:

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

Y'all should observe the latest version of Python 2.x starts.

If y'all see the following error, you lot exercise non have the launcher installed:

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

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

You should come across the currently installed versions of Python.

4.8.1.2. Virtual environments¶

New in version 3.5.

If the launcher is run with no explicit Python version specification, and a virtual environment (created with the standard library 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.

four.8.i.three. From a script¶

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

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

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

Yous should discover the version number of your latest Python 2.x installation is printed. Now endeavour changing the first line to exist:

Re-executing the command should at present impress the latest Python 3.x information. As with the above command-line examples, you lot can specify a more explicit version qualifier. Assuming you lot have Python two.6 installed, endeavour changing the start line to #! python2.6 and you should notice the 2.6 version information printed.

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

iv.eight.1.4. From file associations¶

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

The key do good of this is that a unmarried launcher tin can support multiple Python versions at the aforementioned time depending on the contents of the first line.

4.8.2. Shebang Lines¶

If the showtime line of a script file starts with #! , information technology is known equally 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 bespeak how a script should be executed. This launcher allows the aforementioned facilities to be used with Python scripts on Windows and the examples above demonstrate their use.

To permit 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

The default Python will be located and used. Equally many Python scripts written to work on Unix will already have this line, you should notice these scripts can be used past the launcher without modification. If you are writing a new script on Windows which you hope will exist useful on Unix, you lot should use ane 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" subsequently the pocket-size version. I.e. /usr/bin/python2.7-32 will request usage of the 32-bit python two.7.

New in version 3.7: Beginning with python launcher 3.7 it is possible to request 64-bit version past 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 course of shebang line has one farther special property. Before looking for installed Python interpreters, this form will search the executable PATH for a Python executable. This corresponds to the behaviour of the Unix env plan, which performs a PATH search.

4.8.3. Arguments in shebang lines¶

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

Then Python will exist started with the -v option

4.8.4. Customization¶

iv.eight.4.1. Customization via INI files¶

2 .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 office SHGetFolderPath with CSIDL_LOCAL_APPDATA ) and py.ini in the same directory equally the launcher. The aforementioned .ini files are used for both the 'console' version of the launcher (i.e. py.exe) and for the 'windows' version (i.due east. pyw.exe).

Customization specified in the "application directory" will have precedence over the one adjacent to the executable, so a user, who may non accept write admission to the .ini file next to the launcher, can override commands in that global .ini file.

4.8.4.2. Customizing default Python versions¶

In some cases, a version qualifier can exist included in a command to dictate which version of Python volition exist used past the control. A version qualifier starts with a major version number and tin can optionally be followed by a catamenia ('.') and a pocket-sized version specifier. Furthermore it is possible to specify if a 32 or 64 bit implementation shall be requested past adding "-32" or "-64".

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

If no version qualifiers are institute in a control, the environs variable 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 control line, such as "iii", "3.7", "iii.seven-32" or "3.7-64". (Note that the "-64" pick 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 electric current major version qualifier equally adamant 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 institute for the major version, which is likely, although non guaranteed, to be the near recently installed version in that family.

On 64-fleck Windows with both 32-bit and 64-bit implementations of the aforementioned (major.minor) Python version installed, the 64-fleck version will always be preferred. This will be true for both 32-bit and 64-scrap implementations of the launcher - a 32-fleck launcher will prefer to execute a 64-fleck Python installation of the specified version if bachelor. This is so the behavior of the launcher can exist predicted knowing but what versions are installed on the PC and without regard to the social club in which they were installed (i.e., without knowing whether a 32 or 64-bit version of Python and corresponding launcher was installed last). Every bit noted in a higher place, 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 utilise the latest Python 2.x version installed and the command python3 will use the latest Python three.x installed.
The commands python3.1 and python2.7 will non consult any options at all every bit the versions are fully specified.
If PY_PYTHON=3 , the commands python and python3 will both use the latest installed Python three version.
If PY_PYTHON=iii.1-32 , the control python will use the 32-bit implementation of 3.i 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.one , the commands python and python3 will both use specifically 3.1

In add-on to environment variables, the same settings can exist configured in the .INI file used by the launcher. The section in the INI file is chosen [defaults] and the central proper noun 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 instance:

Setting PY_PYTHON=iii.ane is equivalent to the INI file containing:

Setting PY_PYTHON=3 and PY_PYTHON3=three.i is equivalent to the INI file containing:

                                    [defaults]                                    python                  =                  3                                    python3                  =                  3.1

4.viii.v. Diagnostics¶

If an surroundings 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 yous to meet what versions of Python were located, why a particular version was chosen and the exact command-line used to execute the target Python.

iv.9. Finding modules¶

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

To completely override sys.path , create a ._pth file with the same name every bit the DLL ( python37._pth ) or the executable ( python._pth ) and specify one line for each path to add to sys.path . The file based on the DLL proper 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 style is enabled, and site is non 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 capricious code cannot exist specified.

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

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

An empty entry is added at the start, which corresponds to the current directory.
If the environs variable PYTHONPATH exists, as described in Environment variables, 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 bulldoze identifiers ( C:\ etc.).
Boosted "application paths" can be added in the registry as subkeys of \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 exist added to sys.path . (Annotation that all known installers only utilize HKLM, so HKCU is typically empty.)
If the environment variable PYTHONHOME is set up, information technology is assumed as "Python Home". Otherwise, the path of the main Python executable is used to locate a "landmark file" (either Lib\bone.py or pythonXY.zip ) to deduce the "Python Home". If a Python home is found, the relevant sub-directories added to 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 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 master executable or in the directory ane level above the executable, the following variations use:

If habitation is an absolute path and PYTHONHOME is not ready, this path is used instead of the path to the main executable when deducing the home location.

The stop effect of all this is:

When running python.exe , or any other .exe in the primary Python directory (either an installed version, or directly from the PCbuild directory), the core path is deduced, and the cadre paths in the registry are ignored. Other "application paths" in the registry are ever 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 tin can't find its home and there are no registry value (frozen .exe, some very strange installation setup) you go a path with some default, just relative, paths.

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

Include a ._pth file alongside your executable containing the directories to include. This volition ignore paths listed in the registry and environment variables, and too ignore site unless import site is listed.
If you lot are loading python3.dll or python37.dll in your own executable, explicitly call Py_SetPath() or (at least) Py_SetProgramName() earlier Py_Initialize() .
Clear and/or overwrite PYTHONPATH and set PYTHONHOME before launching python.exe from your awarding.
If y'all cannot use the previous suggestions (for example, y'all are a distribution that allows people to run python.exe directly), ensure that the landmark file ( Lib\os.py ) exists in your install directory. (Note that information technology will not be detected inside a ZIP file, simply a correctly named ZIP file will exist detected instead.)

These will ensure that the files in a system-broad installation will non take precedence over the copy of the standard library bundled with your application. Otherwise, your users may experience problems using your application. Notation that the starting time suggestion is the best, every bit the others may still be susceptible to non-standard paths in the registry and user site-packages.

Inverse in version 3.half dozen:

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 since version iii.6:

Modules specified in the registry under Modules (non PythonPath ) may be imported past importlib.machinery.WindowsRegistryFinder . This finder is enabled on Windows in 3.6.0 and before, but may need to be explicitly added to sys.meta_path in the hereafter.

4.x. Additional modules¶

Fifty-fifty though Python aims to exist portable among all platforms, in that location are features that are unique to Windows. A couple of modules, both in the standard library and external, and snippets exist to employ these features.

The Windows-specific standard modules are documented in MS Windows Specific Services.

iv.10.1. PyWin32¶

The PyWin32 module by Mark Hammond is a collection of modules for advanced Windows-specific support. This includes utilities for:

Component Object Model (COM)
Win32 API calls
Registry
Effect log
Microsoft Foundation Classes (MFC) user interfaces

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

4.10.2. cx_Freeze¶

cx_Freeze is a distutils extension (see Extending Distutils) which wraps Python scripts into executable Windows programs ( * .exe files). When you take done this, you tin can distribute your application without requiring your users to install Python.

four.10.3. WConio¶

Since Python'southward advanced last treatment layer, curses , is restricted to Unix-like systems, there is a library exclusive to Windows as well: Windows Console I/O for Python.

WConio is a wrapper for Turbo-C'southward CONIO.H , used to create text user interfaces.

iv.11. Compiling Python on Windows¶

If you want to compile CPython yourself, offset thing you should do is get the source. You tin download either the latest release'southward source or just grab a fresh 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 PCbuild directory.

Cheque PCbuild/readme.txt for general information on the build process.

For extension modules, consult Edifice C and C++ Extensions on Windows.

Come across besides

Python + Windows + distutils + SWIG + gcc MinGW: 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

4.12. Other Platforms¶

With ongoing development of Python, some platforms that used to exist supported earlier are no longer supported (due to the lack of users or developers). Cheque PEP 11 for details on all unsupported platforms.

Windows CE is still supported.
The Cygwin installer offers to install the Python interpreter too (cf. Cygwin package source, Maintainer releases)

See Python for Windows for detailed information about platforms with pre-compiled installers.