This document aims to give an overview of Windows-specific behaviour you should know about when using Python on Microsoft Windows.
Unlike most Unix systems and services, Windows does not require Python natively and thus does not pre-install a version of Python. However, the CPython team has compiled Windows installers (MSI packages) with every release for many years.
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.
See Python for Windows (and DOS) for detailed information about platforms with precompiled installers.
Besides the standard CPython distribution, there are modified packages including additional functionality. The following is a list of popular versions and their key features:
Notice that these packages are likely to install older versions of Python.
In order to run Python flawlessly, you might have to change certain environment settings in Windows.
Windows has a built-in dialog for changing environment variables (following guide applies to XP classical view): Right-click the icon for your machine (usually located on your Desktop and called “My Computer”) and choose Properties there. Then, open the Advanced tab and click the Environment Variables button.
In short, your path is:
My Computer ‣ Properties ‣ Advanced ‣ Environment Variables
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).
Another way of adding variables to your environment is using the set command:
To make this setting permanent, you could add the corresponding command line to your autoexec.bat. msconfig is a graphical interface to this file.
Viewing environment variables can also be done more straight-forward: The command prompt will expand strings wrapped into percent signs automatically:
Consult set /? for details on this behaviour.
Besides using the automatically created start menu entry for the Python interpreter, you might want to start Python in the DOS prompt. To make this work, you need to set your %PATH% environment variable to include the directory of your Python distribution, delimited by a semicolon from other entries. An example variable could look like this (assuming the first two entries are Windows’ default):
Typing python on your command prompt will now fire up the Python interpreter. Thus, you can also execute your scripts with command line options, see Command line documentation.
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\.
You can add folders to your search path to make Python’s import mechanism search in these directories as well. Use PYTHONPATH, as described in Environment variables, to modify sys.path. On Windows, paths are separated by semicolons, though, to distinguish them from drive identifiers (C:\ etc.).
Modifying the module search path can also be done through the Windows registry under the key HKLM\SOFTWARE\Python\PythonCore\version\PythonPath. Subkeys which have semicolon-delimited path strings as their default value will cause each path to be searched. Multiple subkeys can be created and are appended to the path in alphabetical order. A convenient registry editor is regedit (start it by typing “regedit” into Start ‣ Run).
Python scripts (files with the extension .py) will be executed by python.exe by default. This executable opens a terminal, which stays open even if the program uses a GUI. If you do not want this to happen, use the extension .pyw which will cause the script to be executed by pythonw.exe by default (both executables are located in the top-level of your Python installation directory). This suppresses the terminal window on startup.
You can also make all .py scripts execute with pythonw.exe, setting this through the usual facilities, for example (might require administrative rights):
Launch a command prompt.
Associate the correct file group with .py scripts:
Redirect all Python files to the new executable:
ftype Python.File=C:\Path\to\pythonw.exe "%1" %*
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.
The PyWin32 module by Mark Hammond is a collection of modules for advanced Windows-specific support. This includes utilities for:
PythonWin is a sample MFC application shipped with PyWin32. It is an embeddable IDE with a built-in debugger.
Py2exe 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.
For Microsoft Visual C++, which is the compiler with which official Python releases are built, the source tree contains solutions/project files. View the readme.txt in their respective directories:
|Directory||MSVC version||Visual Studio version|
Note that not all of these build directories are fully supported. Read the release notes to see which compiler version the official releases for your version are built with.
Check PC/readme.txt for general information on the build process.
For extension modules, consult Building C and C++ Extensions on Windows.