
Using Python on Windows
***********************

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


Installing Python
=================

Unlike most Unix systems and services, Windows does not include a
system supported installation of Python. To make Python available, the
CPython team has compiled Windows installers (MSI packages) with every
release for many years. These installers are primarily intended to add
a system-wide installation of Python, with the core interpreter and
library being shared by all application. Non-shared layouts of the
Python interpreter may also be created with the same installer,
however, the released installer is not intended for embedding in other
installers.


Installation Steps
------------------

Four Python 3.5 installers are available for download - two each for
the 32-bit and 64-bit versions of the interpreter. The *web installer*
is a small initial download, and it 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, one of three options may be selected:

[image]

If you select "Install for All Users":

* You may be required to provide administrative credentials or
  approval

* Python will be installed into your Program Files directory

* The *Python Launcher for Windows* will be installed into your
  Windows directory

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

* After installation, the standard library will be pre-compiled to
  bytecode

* If selected, the install directory will be added to "PATH"

If you select "Install Just for Me":

* You will *not* need to be an administrator

* Python will be installed into your user directory

* The *Python Launcher for Windows* will *also* be installed into
  your user directory

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

* If selected, the install directory will be added to "PATH"

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


Installing Without UI
---------------------

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

To completely hide the installer UI and install Python silently, pass
the "/quiet" ("/q") option. To skip past the user interaction but
still display progress and errors, pass the "/passive" ("/p") option.
The "/uninstall" option may be passed to immediately begin removing
Python - no prompt will be displayed.

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

+-----------------------------+----------------------------------------+----------------------------+
| Name                        | Description                            | Default                    |
+=============================+========================================+============================+
| InstallAllUsers             | Perform a system-wide installation.    | 1                          |
+-----------------------------+----------------------------------------+----------------------------+
| TargetDir                   | The installation directory             | Selected based on          |
|                             |                                        | InstallAllUsers            |
+-----------------------------+----------------------------------------+----------------------------+
| DefaultAllUsersTargetDir    | The default installation directory for | "%ProgramFiles%\Python     |
|                             | all-user installs                      | X.Y" or "%ProgramFiles(x8  |
|                             |                                        | 6)%\Python X.Y"            |
+-----------------------------+----------------------------------------+----------------------------+
| DefaultJustForMeTargetDir   | The default install directory for      | "%LocalAppData%\Programs\  |
|                             | just-for-me installs                   | PythonXY" or "%LocalAppDa  |
|                             |                                        | ta%\Programs\PythonXY-32"  |
+-----------------------------+----------------------------------------+----------------------------+
| DefaultCustomTargetDir      | The default custom install directory   | (empty)                    |
|                             | displayed in the UI                    |                            |
+-----------------------------+----------------------------------------+----------------------------+
| AssociateFiles              | Create file associations if the        | 1                          |
|                             | launcher is also installed.            |                            |
+-----------------------------+----------------------------------------+----------------------------+
| CompileAll                  | Compile all ".py" files to ".pyc" and  | 0                          |
|                             | ".pyo".                                |                            |
+-----------------------------+----------------------------------------+----------------------------+
| PrependPath                 | Add install and Scripts directories    | 0                          |
|                             | tho "PATH" and ".PY" to "PATHEXT"      |                            |
+-----------------------------+----------------------------------------+----------------------------+
| Include_doc                 | Install Python manual                  | 1                          |
+-----------------------------+----------------------------------------+----------------------------+
| Include_debug               | Install debug binaries                 | 0                          |
+-----------------------------+----------------------------------------+----------------------------+
| Include_dev                 | Install developer headers and          | 1                          |
|                             | libraries                              |                            |
+-----------------------------+----------------------------------------+----------------------------+
| Include_exe                 | Install "python.exe" and related files | 1                          |
+-----------------------------+----------------------------------------+----------------------------+
| Include_launcher            | Install *Python Launcher for Windows*. | 1                          |
+-----------------------------+----------------------------------------+----------------------------+
| Include_lib                 | Install standard library and extension | 1                          |
|                             | modules                                |                            |
+-----------------------------+----------------------------------------+----------------------------+
| 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                          |
+-----------------------------+----------------------------------------+----------------------------+
| SimpleInstall               | Disable most install UI                | 0                          |
+-----------------------------+----------------------------------------+----------------------------+

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

   python-3.5.0.exe /quiet InstallAllUsers=1 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:

   python-3.5.0.exe /passive InstallAllUsers=0 Include_launcher=0 Include_test=0 SimpleInstall=1

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


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 this need, all possible components may be downloaded on-
demand to create a complete *layout* that will no longer require an
internet connection regardless of the selected features. Note that
this download may be bigger than required, but where a large number of
installations are going to be performed it is very useful to have a
locally cached copy.

Execute the following command from Command Prompt to download all
possible required files.  Remember to substitute "python-3.5.0.exe"
for the actual name of your installer, and to create layouts in their
own directories to avoid collisions between files with the same name.

   python-3.5.0.exe /layout [optional target directory]

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


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 **PEP 11** for details on all unsupported
platforms.

* Windows CE is still supported.

* The Cygwin installer offers to install the Python interpreter as
  well (cf. Cygwin package source, Maintainer releases)

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

See also: Python on XP

     "7 Minutes to "Hello World!"" by Richard Dooling, 2006

  Installing on Windows
     in "Dive into Python: Python from novice to pro" by Mark Pilgrim,
     2004, ISBN 1-59059-356-1

  For Windows users
     in "Installing Python" in "A Byte of Python" by Swaroop C H, 2003


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:

ActivePython
   Installer with multi-platform compatibility, documentation, PyWin32

Anaconda
   Popular scientific modules (such as 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 building packages.

Note that these packages may not include the latest versions of Python
or other libraries, and are not maintained or supported by the core
Python team.


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 *Python Launcher for Windows*.


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 **set** command:

   C:\>set PATH=C:\Program Files\Python 3.5;%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 "PATH" by adding the directory containing
**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, *Advanced system settings* and click the *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
  "PATH".The "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 all of your
  installed Python versions.

See also: http://support.microsoft.com/kb/100843

     Environment variables in Windows NT

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

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

  http://support.microsoft.com/kb/310519
     How To Manage Environment Variables in Windows XP

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


Finding the Python executable
-----------------------------

Changed in version 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 for Python 3.5 and later has an option to set
that up for you.

On the first page of the installer, an option labelled "Add Python 3.5
to PATH" can be selected to have the installer add the install
location into the "PATH".  The location of the "Scripts\" folder is
also added. This allows you to type **python** to run the interpreter,
and **pip** or . Thus, you can also execute your scripts with command
line options, see *Command line* 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 "PATH" using the directions in *Excursus: Setting
environment variables*.  You need to set your "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 3.5


Python Launcher for Windows
===========================

New in version 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 "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.


Getting started
---------------


From the command-line
~~~~~~~~~~~~~~~~~~~~~

System-wide installations of Python 3.3 and later will put the
launcher on your "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 2.x 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 2.x installed (e.g., 2.6 and
2.7) you will have noticed that Python 2.7 was started - to launch
Python 2.6, try the command:

   py -2.6

If you have a Python 3.x installed, try the command:

   py -3

You should find the latest version of Python 3.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 "PATH"
unless the option was selected on installation.


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.


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.


From file associations
~~~~~~~~~~~~~~~~~~~~~~

The launcher should have been associated with Python files (i.e.
".py", ".pyw", ".pyc", ".pyo" 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 are commonly used on such systems to
indicate how a script should be executed.  This launcher allows the
same facilities to be using 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) - for example "/usr/bin/python2.7" - which will cause that
specific version to be located and used.

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 "PATH" for a Python executable. This
corresponds to the behaviour of the Unix "env" program, which performs
a "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. If the minor
qualifier is specified, it may optionally be followed by "-32" to
indicate the 32-bit implementation of that version be used.

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 "PY_PYTHON" can be set to specify the default version
qualifier - the default value is "2". Note this value could specify
just a major version (e.g. "2") or a major.minor qualifier (e.g.
"2.6"), or even major.minor-32.

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" 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 "C:\Python\", the default library would reside in
"C:\Python\Lib\" and third-party modules should be stored in
"C:\Python\Lib\site-packages\".

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 environment 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 drive identifiers ("C:\"
  etc.).

* Additional "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 be added to "sys.path".  (Note that all
  known installers only use HKLM, so HKCU is typically empty.)

* If the environment variable "PYTHONHOME" is set, it is assumed as
  "Python Home".  Otherwise, the path of the main Python executable is
  used to locate a "landmark file" ("Lib\os.py") to deduce the "Python
  Home".  If a Python home is found, the relevant sub-directories
  added to "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).

The end result of all this is:

* When running "python.exe", or any other .exe in the main Python
  directory (either an installed version, or directly from the PCbuild
  directory), the core path is deduced, and the core paths in the
  registry are ignored.  Other "application paths" in the registry are
  always read.

* When Python is hosted in another .exe (different directory,
  embedded via COM, etc), the "Python Home" will not be deduced, so
  the core path from the registry is used.  Other "application paths"
  in the registry are always read.

* If Python can't find its home and there is no registry (eg, frozen
  .exe, some very strange installation setup) you get a path with some
  default, but relative, paths.

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

* If you are loading "python3.dll" or "python35.dll" in your own
  executable, explicitly call "Py_SetPath()" or (at least)
  "Py_SetProgramName()" before "Py_Initialize()".

* Clear and/or overwrite "PYTHONPATH" and set "PYTHONHOME" before
  launching "python.exe" from your application.

* If you cannot use the previous suggestions (for example, you are a
  distribution that allows people to run "python.exe" directly),
  ensure that the landmark file ("Lib\os.py") exists in your bundled
  library. (Note that it will not be detected inside a ZIP file.)

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.


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 *MS Windows
Specific Services*.


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

* Event log

* Microsoft Foundation Classes (MFC) user interfaces

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

See also: Win32 How Do I...?

     by Tim Golden

  Python and COM
     by David and Paul Boddie


cx_Freeze
---------

cx_Freeze is a "distutils" extension (see *Extending Distutils*) which
wraps Python scripts into executable Windows programs ("***.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, "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's "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 source. You can download either the latest release's 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.

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

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

See also: 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

  MingW -- Python extensions
     by Trent Apted et al, 2007


Other resources
===============

See also: Python Programming On Win32

     "Help for Windows Programmers" by Mark Hammond and Andy Robinson,
     O'Reilly Media, 2000, ISBN 1-56592-621-8

  A Python for Windows Tutorial
     by Amanda Birmingham, 2004

  **PEP 397** - Python launcher for Windows
     The proposal for the launcher to be included in the Python
     distribution.
