4.1.1.Installation¶

The Python install manager can be installed from theMicrosoft Store appor downloaded and installed frompython.org/downloads. The two versions areidentical.

To install through the Store, simply click “Install”. After it has completed,open a terminal and typepython to get started.

To install the file downloaded from python.org, either double-click and select“Install”, or runAdd-AppxPackage<pathtoMSIX> in Windows Powershell.

After installation, thepython,py, andpymanager commands should beavailable. If you have existing installations of Python, or you have modifiedyourPATH variable, you may need to remove them or undo themodifications. SeeTroubleshooting for more help with fixingnon-working commands.

When you first install a runtime, you will likely be prompted to add a directoryto yourPATH. This is optional, if you prefer to use thepycommand, but is offered for those who prefer the full range of aliases (suchaspython3.14.exe) to be available. The directory will be%LocalAppData%\Python\bin by default, but may be customized by anadministrator. Click Start and search for “Edit environment variables for youraccount” for the system settings page to add the path.

Each Python runtime you install will have its own directory for scripts. Thesealso need to be added toPATH if you want to use them.

The Python install manager will be automatically updated to new releases. Thisdoes not affect any installs of Python runtimes. Uninstalling the Python installmanager does not uninstall any Python runtimes.

If you are not able to install an MSIX in your context, for example, you areusing automated deployment software that does not support it, or are targetingWindows Server 2019, please seeAdvanced Installation below for moreinformation.

4.1.2.Basic Use¶

The recommended command for launching Python ispython, which will eitherlaunch the version requested by the script being launched, an active virtualenvironment, or the default installed version, which will be the latest stablerelease unless configured otherwise. If no version is specifically requested andno runtimes are installed at all, the current latest release will be installedautomatically.

For all scenarios involving multiple runtime versions, the recommended commandispy. This may be used anywhere in place ofpython or the olderpy.exe launcher. By default,py matches the behaviour ofpython, butalso allows command line options to select a specific version as well assubcommands to manage installations. These are detailed below.

Because thepy command may already be taken by the previous version, thereis also an unambiguouspymanager command. Scripted installs that areintending to use Python install manager should consider usingpymanager, dueto the lower chance of encountering a conflict with existing installs. The onlydifference between the two commands is when running without any arguments:py will install and launch your default interpreter, whilepymanagerwill display help (pymanagerexec... provides equivalent behaviour topy...).

Each of these commands also has a windowed version that avoids creating aconsole window. These arepyw,pythonw andpymanagerw. Apython3command is also included that mimics thepython command. It is intended tocatch accidental uses of the typical POSIX command on Windows, but is not meantto be widely used or recommended.

To launch your default runtime, runpython orpy with the arguments youwant to be passed to the runtime (such as script files or the module to launch):

$> py...$> python my-script.py...$> py -m this...

The default runtime can be overridden with thePYTHON_MANAGER_DEFAULTenvironment variable, or a configuration file. SeeConfiguration forinformation about configuration settings.

To launch a specific runtime, thepy command accepts a-V:<TAG> option.This option must be specified before any others. The tag is part or all of theidentifier for the runtime; for those from the CPython team, it looks like theversion, potentially with the platform. For compatibility, theV: may beomitted in cases where the tag refers to an official release and starts with3.

$> py -V:3.14 ...$> py -V:3-arm64 ...

Runtimes from other distributors may require thecompany to be included aswell. This should be separated from the tag by a slash, and may be a prefix.Specifying the company is optional when it isPythonCore, and specifying thetag is optional (but not the slash) when you want the latest release from aspecific company.

$> py -V:Distributor\1.0 ...$> py -V:distrib/ ...

If no version is specified, but a script file is passed, the script will beinspected for ashebang line. This is a special format for the first line ina file that allows overriding the command. SeeShebang lines for moreinformation. When there is no shebang line, or it cannot be resolved, the scriptwill be launched with the default runtime.

If you are running in an active virtual environment, have not requested aparticular version, and there is no shebang line, the default runtime will bethat virtual environment. In this scenario, thepython command was likelyalready overridden and none of these checks occurred. However, this behaviourensures that thepy command can be used interchangeably.

When you launch eitherpython orpy but do not have any runtimesinstalled, and the requested version is the default, it will be installedautomatically and then launched. Otherwise, the requested version will beinstalled if automatic installation is configured (most likely by settingPYTHON_MANAGER_AUTOMATIC_INSTALL totrue), or if thepyexec orpymanagerexec forms of the command were used.

4.1.3.Command Help¶

Thepyhelp command will display the full list of supported commands, alongwith their options. Any command may be passed the-? option to display itshelp, or its name passed topyhelp.

$> py help$> py help install$> py install /?

All commands support some common options, which will be shown bypyhelp.These options must be specified after any subcommand. Specifying-v or--verbose will increase the amount of output shown, and-vv willincrease it further for debugging purposes. Passing-q or--quiet willreduce output, and-qq will reduce it further.

The--config=<PATH> option allows specifying a configuration file tooverride multiple settings at once. SeeConfiguration below for moreinformation about these files.

4.1.4.Listing Runtimes¶

$> py list [-f=|--format=<FMT>] [-1|--one] [--online|-s=|--source=<URL>] [<TAG>...]

The list of installed runtimes can be seen usingpylist. A filter may beadded in the form of one or more tags (with or without company specifier), andeach may include a<,<=,>= or> prefix to restrict to a range.

A range of formats are supported, and can be passed as the--format=<FMT> or-f<FMT> option. Formats includetable (a user friendly table view),csv (comma-separated table),json (a single JSON blob),jsonl (oneJSON blob per result),exe (just the executable path),prefix (just theprefix path).

The--one or-1 option only displays a single result. If the defaultruntime is included, it will be the one. Otherwise, the “best” result is shown(“best” is deliberately vaguely defined, but will usually be the most recentversion). The result shown bypylist--one<TAG> will match the runtimethat would be launched bypy-V:<TAG>.

The--only-managed option excludes results that were not installed by thePython install manager. This is useful when determining which runtimes may beupdated or uninstalled through thepy command.

The--online option is short for passing--source=<URL> with the defaultsource. Passing either of these options will search the online index forruntimes that can be installed. The result shown bypylist--online--one<TAG> will match the runtime that would be installed bypyinstall<TAG>.

$> py list --online 3.14

For compatibility with the old launcher, the--list,--list-paths,-0 and-0p commands (e.g.py-0p) are retained. They do not allowadditional options, and will produce legacy formatted output.

4.1.5.Installing Runtimes¶

$> py install [-s=|--source=<URL>] [-f|--force] [-u|--update] [--dry-run] [<TAG>...]

New runtime versions may be added usingpyinstall. One or more tags may bespecified, and the special tagdefault may be used to select the default.Ranges are not supported for installation.

The--source=<URL> option allows overriding the online index that is used toobtain runtimes. This may be used with an offline index, as shown inOffline Installs.

Passing--force will ignore any cached files and remove any existing installto replace it with the specified one.

Passing--update will replace existing installs if the new version is newer.Otherwise, they will be left. If no tags are provided with--update, allinstalls managed by the Python install manager will be updated if newer versionsare available. Updates will remove any modifications made to the install,including globally installed packages, but virtual environments will continue towork.

Passing--dry-run will generate output and logs, but will not modify anyinstalls.

In addition to the above options, the--target option will extract theruntime to the specified directory instead of doing a normal install. This isuseful for embedding runtimes into larger applications.

$> py install ... [-t=|--target=<PATH>] <TAG>

4.1.6.Offline Installs¶

To perform offline installs of Python, you will need to first create an offlineindex on a machine that has network access.

$> py install --download=<PATH> ... <TAG>...

The--download=<PATH> option will download the packages for the listed tagsand create a directory containing them and anindex.json file suitable forlater installation. This entire directory can be moved to the offline machineand used to install one or more of the bundled runtimes:

$> py install --source="<PATH>\index.json" <TAG>...

The Python install manager can be installed by downloading its installer andmoving it to another machine before installing.

Alternatively, the ZIP files in an offline index directory can simply betransferred to another machine and extracted. This will not register the installin any way, and so it must be launched by directly referencing the executablesin the extracted directory, but it is sometimes a preferable approach in caseswhere installing the Python install manager is not possible or convenient.

In this way, Python runtimes can be installed and managed on a machine withoutaccess to the internet.

4.1.7.Uninstalling Runtimes¶

$> py uninstall [-y|--yes] <TAG>...

Runtimes may be removed using thepyuninstall command. One or more tagsmust be specified. Ranges are not supported here.

The--yes option bypasses the confirmation prompt before uninstalling.

Instead of passing tags individually, the--purge option may be specified.This will remove all runtimes managed by the Python install manager, includingcleaning up the Start menu, registry, and any download caches. Runtimes thatwere not installed by the Python install manager will not be impacted, andneither will manually created configuration files.

$> py uninstall [-y|--yes] --purge

The Python install manager can be uninstalled through the Windows “Installedapps” settings page. This does not remove any runtimes, and they will still beusable, though the globalpython andpy commands will be removed.Reinstalling the Python install manager will allow you to manage these runtimesagain. To completely clean up all Python runtimes, run with--purge beforeuninstalling the Python install manager.

4.1.8.Configuration¶

Python install manager is configured with a hierarchy of configuration files,environment variables, command-line options, and registry settings. In general,configuration files have the ability to configure everything, including thelocation of other configuration files, while registry settings areadministrator-only and will override configuration files. Command-line optionsoverride all other settings, but not every option is available.

This section will describe the defaults, but be aware that modified oroverridden installs may resolve settings differently.

A global configuration file may be configured by an administrator, and would beread first. The user configuration file is stored at%AppData%\Python\pymanager.json (by default) and is read next,overwriting any settings from earlier files. An additional configuration filemay be specified as thePYTHON_MANAGER_CONFIG environment variable or the--config command line option (but not both).

The following settings are those that are considered likely to be modified innormal use. Later sections list those that are intended for administrativecustomization.

Dotted names should be nested inside JSON objects, for example,list.formatwould be specified as{"list":{"format":"table"}}.

4.1.9.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 nativesupport for such lines and they are commonly used on such systems to indicatehow a script should be executed. Thepython andpy commands allow thesame facilities to be used with Python scripts on Windows.

To allow shebang lines in Python scripts to be portable between Unix andWindows, a number of ‘virtual’ commands are supported to specify whichinterpreter to use. The supported virtual commands are:

• /usr/bin/env<ALIAS>

• /usr/bin/env-S<ALIAS>

• /usr/bin/<ALIAS>

• /usr/local/bin/<ALIAS>

• <ALIAS>

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

#! /usr/bin/python

The default Python or an active virtual environment 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 onUnix, you should use one of the shebang lines starting with/usr.

Any of the above virtual commands can have<ALIAS> replaced by an alias froman installed runtime. That is, any command generated in the global aliasesdirectory (which you may have added to yourPATH environment variable)can be used in a shebang, even if it is not on yourPATH. This allowsthe use of shebangs like/usr/bin/python3.12 to select a particular runtime.

If no runtimes are installed, or if automatic installation is enabled, therequested runtime will be installed if necessary. SeeConfigurationfor information about configuration settings.

The/usr/bin/env form of shebang line will also search thePATHenvironment variable for unrecognized commands. This corresponds to thebehaviour of the Unixenv program, which performs the same search, butprefers launching known Python commands. A warning may be displayed whensearching for arbitrary executables, and this search may be disabled by theshebang_can_run_anything configuration option.

Shebang lines that do not match any of patterns are treated asWindowsexecutable paths that are absolute or relative to the directory containing thescript file. This is a convenience for Windows-only scripts, such as thosegenerated by an installer, since the behavior is not compatible with Unix-styleshells. These paths may be quoted, and may include multiple arguments, afterwhich the path to the script and any additional arguments will be appended.This functionality may be disabled by theshebang_can_run_anythingconfiguration option.

4.1.10.Advanced Installation¶

For situations where an MSIX cannot be installed, such as some olderadministrative distribution platforms, there is an MSI available from thepython.org downloads page. This MSI has no user interface, and can only performper-machine installs to its default location in Program Files. It will attemptto modify the systemPATH environment variable to include this installlocation, but be sure to validate this on your configuration.

Be aware that the MSI package does not bundle any runtimes, and so is notsuitable for installs into offline environments without also creating an offlineinstall index. SeeOffline Installs andAdministrative Configurationfor information on handling these scenarios.

Runtimes installed by the MSI are shared with those installed by the MSIX, andare all per-user only. The Python install manager does not support installingruntimes per-machine. To emulate a per-machine install, you can usepyinstall--target=<sharedlocation> as administrator and add your own system-widemodifications toPATH, the registry, or the Start menu.

When the MSIX is installed, but commands are not available in thePATHenvironment variable, they can be found under%LocalAppData%\Microsoft\WindowsApps\PythonSoftwareFoundation.PythonManager_3847v3x7pw1kmor%LocalAppData%\Microsoft\WindowsApps\PythonSoftwareFoundation.PythonManager_qbz5n2kfra8p0,depending on whether it was installed from python.org or through the WindowsStore. Attempting to run the executable directly from Program Files is notrecommended.

To programmatically install the Python install manager, it is easiest to useWinGet, which is included with all supported versions of Windows:

$>wingetinstall9NQ7512CXL7T-e--accept-package-agreements--disable-interactivity# Optionally run the configuration checker and accept all changes$>pyinstall--configure-y

To download the Python install manager and install on another machine, thefollowing WinGet command will download the required files from the Store to yourDownloads directory (add-d<location> to customize the output location).This also generates a YAML file that appears to be unnecessary, as thedownloaded MSIX can be installed by launching or using the commands below.

$>wingetdownload9NQ7512CXL7T-e--skip-license--accept-package-agreements--accept-source-agreements

To programmatically install or uninstall an MSIX using only PowerShell, theAdd-AppxPackage andRemove-AppxPackage PowerShell cmdlets are recommended:

$>Add-AppxPackageC:\Downloads\python-manager-25.0.msix...$>Get-AppxPackagePythonSoftwareFoundation.PythonManager|Remove-AppxPackage

The latest release can be downloaded and installed by Windows by passing theAppInstaller file to the Add-AppxPackage command. This installs using the MSIXon python.org, and is only recommended for cases where installing via the Store(interactively or using WinGet) is not possible.

$>Add-AppxPackage-AppInstallerFilehttps://www.python.org/ftp/python/pymanager/pymanager.appinstaller

Other tools and APIs may also be used to provision an MSIX package for all userson a machine, but Python does not consider this a supported scenario. We suggestlooking into the PowerShellAdd-AppxProvisionedPackage cmdlet, the nativeWindowsPackageManager class, or the documentation and support for yourdeployment tool.

Regardless of the install method, users will still need to install their owncopies of Python itself, as there is no way to trigger those installs withoutbeing a logged in user. When using the MSIX, the latest version of Python willbe available for all users to install without network access.

Note that the MSIX downloadable from the Store and from the Python website aresubtly different and cannot be installed at the same time. Wherever possible,we suggest using the above WinGet commands to download the package from theStore to reduce the risk of setting up conflicting installs. There are nolicensing restrictions on the Python install manager that would prevent usingthe Store package in this way.

4.1.11.Administrative Configuration¶

There are a number of options that may be useful for administrators to overrideconfiguration of the Python install manager. These can be used to provide localcaching, disable certain shortcut types, override bundled content. All of theabove configuration options may be set, as well as those below.

Configuration options may be overridden in the registry by setting values underHKEY_LOCAL_MACHINE\Software\Policies\Python\PyManager, where thevalue name matches the configuration key and the value type isREG_SZ. Notethat this key can itself be customized, but only by modifying the core configfile distributed with the Python install manager. We recommend, however, thatregistry values are used only to setbase_config to a JSON file containingthe full set of overrides. Registry key overrides will replace any otherconfigured setting, whilebase_config allows users to further modifysettings they may need.

Note that most settings with environment variables support those variablesbecause their default setting specifies the variable. If you override them, theenvironment variable will no longer work, unless you override it with anotherone. For example, the default value ofconfirm is literally%PYTHON_MANAGER_CONFIRM%, which will resolve the variable at load time. Ifyou override the value toyes, then the environment variable will no longerbe used. If you override the value to%CONFIRM%, then that environmentvariable will be used instead.

Configuration settings that are paths are interpreted as relative to thedirectory containing the configuration file that specified them.

4.1.12.Installing Free-threaded Binaries¶

Pre-built distributions of the experimental free-threaded build are availableby installing tags with thet suffix.

$> py install 3.14t$> py install 3.14t-arm64$> py install 3.14t-32

This will install and register as normal. If you have no other runtimesinstalled, thenpython will launch this one. Otherwise, you will need to usepy-V:3.14t... or, if you have added the global aliases directory to yourPATH environment variable, thepython3.14t.exe commands.

4.1.13.Troubleshooting¶

If your Python install manager does not seem to be working correctly, pleasework through these tests and fixes to see if it helps. If not, please report anissue atour bug tracker,including any relevant log files (written to your%TEMP% directory bydefault).

4.2.1.Python Application¶

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

Using a specialized executable as a launcher requires some coding, but providesthe most transparent experience for users. With a customized launcher, there areno obvious indications that the program is running on Python: icons can becustomized, company and version information can be specified, and fileassociations behave properly. In most cases, a custom launcher should simply beable to callPy_Main with a hard-coded command line.

The simpler approach is to provide a batch file or generated shortcut thatdirectly calls thepython.exe orpythonw.exe with the requiredcommand-line arguments. In this case, the application will appear to be Pythonand not its actual name, and users may have trouble distinguishing it from otherrunning Python processes or file associations.

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

4.2.2.Embedding Python¶

Applications written in native code often require some form of scriptinglanguage, and the embedded Python distribution can be used for this purpose. Ingeneral, the majority of the application is in native code, and some part willeither invokepython.exe or directly usepython3.dll. For either case,extracting the embedded distribution to a subdirectory of the applicationinstallation is sufficient to provide a loadable Python interpreter.

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

4.3.1.Free-threaded packages¶

Packages containing free-threaded binaries are namedpython-freethreadedfor the 64-bit version,pythonx86-freethreaded for the 32-bitversion, andpythonarm64-freethreaded for the ARM64version. These packages contain both thepython3.13t.exe andpython.exe entry points, both of which run free threaded.

4.9.1.PyWin32¶

ThePyWin32 module by Mark Hammondis a collection of modules for advanced Windows-specific support. This includesutilities for:

• Component Object Model(COM)

• Win32 API calls

• Registry

• Event log

• Microsoft Foundation Classes(MFC) user interfaces

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

4.9.2.cx_Freeze¶

cx_Freezewraps Python scripts into executable Windows programs(*.exe files). When you have done this, you can distribute yourapplication without requiring your users to install Python.

4.11.1.Installation steps¶

Four Python 3.15 installers are available for download - two each for the32-bit and 64-bit versions of the interpreter. Theweb installer is a smallinitial download, and it will automatically download the required components asnecessary. Theoffline installer includes the components necessary for adefault installation and only requires an internet connection for optionalfeatures. SeeInstalling Without Downloading for other ways to avoid downloadingduring installation.

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

If you select “Install Now”:

• You willnot need to be an administrator (unless a system update for theC Runtime Library is required or you install thePython Install Manager for allusers)

• Python will be installed into your user directory

• ThePython Install Manager will be installed according to the option at the bottomof the first page

• The standard library, test suite, launcher and pip will be installed

• If selected, the install directory will be added to yourPATH

• Shortcuts will only be visible for the current user

Selecting “Customize installation” will allow you to select the features toinstall, the installation location and other options or post-install actions.To install debugging symbols or binaries, you will need to use this option.

To perform an all-users installation, you should select “Customizeinstallation”. In this case:

• You may be required to provide administrative credentials or approval

• Python will be installed into the Program Files directory

• ThePython Install Manager will be installed into the Windows directory

• Optional features may be selected during installation

• The standard library can be pre-compiled to bytecode

• If selected, the install directory will be added to the systemPATH

• Shortcuts are available for all users

4.11.2.Removing the MAX_PATH Limitation¶

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

In the latest versions of Windows, this limitation can be expanded toapproximately 32,000 characters. Your administrator will need to activate the“Enable Win32 long paths” group policy, or setLongPathsEnabled to1in the registry keyHKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem.

This allows theopen() function, theos module and most otherpath functionality to accept and return paths longer than 260 characters.

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

4.11.3.Installing Without UI¶

All of the options available in the installer UI can also be specified from thecommand line, allowing scripted installers to replicate an installation on manymachines without user interaction. These options may also be set withoutsuppressing the UI in order to change some of the defaults.

The following options (found by executing the installer with/?) can bepassed into the installer:

All other options are passed asname=value, where the value is usually0 to disable a feature,1 to enable a feature, or a path. The full listof available options is shown below.

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

python-3.9.0.exe /quiet InstallAllUsers=1 PrependPath=1 Include_test=0

To allow users to easily install a personal copy of Python without the testsuite, you could provide a shortcut with the following command. This willdisplay a simplified initial page and disallow customization:

python-3.9.0.exe InstallAllUsers=0 Include_launcher=0 Include_test=0    SimpleInstall=1 SimpleInstallDescription="Just for me, no test suite."

(Note that omitting the launcher also omits file associations, and is onlyrecommended for per-user installs when there is also a system-wide installationthat included the launcher.)

The options listed above can also be provided in a file namedunattend.xmlalongside the executable. This file specifies a list of options and values.When a value is provided as an attribute, it will be converted to a number ifpossible. Values provided as element text are always left as strings. Thisexample file sets the same options as the previous example:

<Options><OptionName="InstallAllUsers"Value="no"/><OptionName="Include_launcher"Value="0"/><OptionName="Include_test"Value="no"/><OptionName="SimpleInstall"Value="yes"/><OptionName="SimpleInstallDescription">Justforme,notestsuite</Option></Options>

4.11.4.Installing Without Downloading¶

As some features of Python are not included in the initial installer download,selecting those features may require an internet connection. To avoid thisneed, all possible components may be downloaded on-demand to create a completelayout that will no longer require an internet connection regardless of theselected features. Note that this download may be bigger than required, butwhere a large number of installations are going to be performed it is veryuseful to have a locally cached copy.

Execute the following command from Command Prompt to download all possiblerequired files. Remember to substitutepython-3.9.0.exe for the actualname of your installer, and to create layouts in their own directories toavoid collisions between files with the same name.

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

You may also specify the/quiet option to hide the progress display.

4.11.5.Modifying an install¶

Once Python has been installed, you can add or remove features through thePrograms and Features tool that is part of Windows. Select the Python entry andchoose “Uninstall/Change” to open the installer in maintenance mode.

“Modify” allows you to add or remove features by modifying the checkboxes -unchanged checkboxes will not install or remove anything. Some options cannot bechanged in this mode, such as the install directory; to modify these, you willneed to remove and then reinstall Python completely.

“Repair” will verify all the files that should be installed using the currentsettings and replace any that have been removed or modified.

“Uninstall” will remove Python entirely, with the exception of thePython Install Manager, which has its own entry in Programs and Features.

4.11.6.Installing Free-threaded Binaries¶

To install pre-built binaries with free-threading enabled (seePEP 703), youshould select “Customize installation”. The second page of options includes the“Download free-threaded binaries” checkbox.

Selecting this option will download and install additional binaries to the samelocation as the main Python install. The main executable is calledpython3.13t.exe, and other binaries either receive at suffix or a fullABI suffix. Python source files and bundled third-party dependencies are sharedwith the main install.

The free-threaded version is registered as a regular Python install with thetag3.13t (with a-32 or-arm64 suffix as normal for thoseplatforms). This allows tools to discover it, and for thePython Install Manager tosupportpy.exe-3.13t. Note that the launcher will interpretpy.exe-3(or apython3 shebang) as “the latest 3.x install”, which will prefer thefree-threaded binaries over the regular ones, whilepy.exe-3.13 will not.If you use the short style of option, you may prefer to not install thefree-threaded binaries at this time.

To specify the install option at the command line, useInclude_freethreaded=1. SeeInstalling Without Downloading for instructions onpre-emptively downloading the additional binaries for offline install. Theoptions to include debug symbols and binaries also apply to the free-threadedbuilds.

Free-threaded binaries are also availableon nuget.org.

4.12.1.Getting started¶

py

py -3.7

py -2

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

py --list

# Select any '3.*' tagged runtimepy -V:3# Select any 'PythonCore' released runtimepy -V:PythonCore/# Select PythonCore's latest Python 3 runtimepy -V:PythonCore/3

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

py hello.py

#! python3

4.12.2.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 nativesupport for such lines and they are commonly used on such systems to indicatehow a script should be executed. This launcher allows the same facilities tobe used with Python scripts on Windows and the examples above demonstrate theiruse.

To allow shebang lines in Python scripts to be portable between Unix andWindows, this launcher supports a number of ‘virtual’ commands to specifywhich interpreter to use. The supported virtual commands are:

• /usr/bin/env

• /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 or an active virtual environment 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 onUnix, 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 theminor version. I.e./usr/bin/python3.7-32 will request usage of the32-bit Python 3.7. If a virtual environment is active, the version will beignored and the environment will be used.

The/usr/bin/env form of shebang line has one further special property.Before looking for installed Python interpreters, this form will search theexecutablePATH for a Python executable matching the name providedas the first argument. This corresponds to the behaviour of the Unixenvprogram, which performs aPATH search.If an executable matching the first argument after theenv command cannotbe found, but the argument starts withpython, it will be handled asdescribed for the other virtual commands.The environment variablePYLAUNCHER_NO_SEARCH_PATH may be set(to any value) to skip this search ofPATH.

Shebang lines that do not match any of these patterns are looked up in the[commands] section of the launcher’s.INI file.This may be used to handle certain commands in a way that makes sense for yoursystem. The name of the command must be a single argument (no spaces in theshebang executable), and the value substituted is the full path to theexecutable (additional arguments specified in the .INI will be quoted as partof the filename).

[commands]/bin/xpython=C:\Program Files\XPython\python.exe

Any commands not found in the .INI file are treated asWindows executablepaths that are absolute or relative to the directory containing the script file.This is a convenience for Windows-only scripts, such as those generated by aninstaller, since the behavior is not compatible with Unix-style shells.These paths may be quoted, and may include multiple arguments, after which thepath to the script and any additional arguments will be appended.

4.12.3.Arguments in shebang lines¶

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

#! /usr/bin/python -v

Then Python will be started with the-v option

4.12.4.Customization¶

[defaults]python=3.7

[defaults]python=3python3=3.7

4.12.5.Diagnostics¶

If an environment variablePYLAUNCHER_DEBUG is set (to any value), thelauncher will print diagnostic information to stderr (i.e. to the console).While this information manages to be simultaneously verboseand terse, itshould allow you to see what versions of Python were located, why aparticular version was chosen and the exact command-line used to execute thetarget Python. It is primarily intended for testing and debugging.

4.12.6.Dry Run¶

If an environment variablePYLAUNCHER_DRYRUN is set (to any value),the launcher will output the command it would have run, but will not actuallylaunch Python. This may be useful for tools that want to use the launcher todetect and then launch Python directly. Note that the command written tostandard output is always encoded using UTF-8, and may not render correctly inthe console.

4.12.7.Install on demand¶

If an environment variablePYLAUNCHER_ALLOW_INSTALL is set (to anyvalue), and the requested Python version is not installed but is available onthe Microsoft Store, the launcher will attempt to install it. This may requireuser interaction to complete, and you may need to run the command again.

An additionalPYLAUNCHER_ALWAYS_INSTALL variable causes the launcherto always try to install Python, even if it is detected. This is mainly intendedfor testing (and should be used withPYLAUNCHER_DRYRUN).

4.12.8.Return codes¶

The following exit codes may be returned by the Python launcher. Unfortunately,there is no way to distinguish these from the exit code of Python itself.

The names of codes are as used in the sources, and are only for reference. Thereis no way to access or resolve them apart from reading this page. Entries arelisted in alphabetical order of names.