Skip to main content

Lightweight python 2.5-3.3 launcher and switcher for Windows command line and MSYS/MINGW32. Partly PEP 397 compliant.

Project description

pywin is a lightweight python 2.5-3.3 launcher and switcher for Windows command line and MSYS/MINGW32. It’s similar to the py.exe launcher/switcher available in python 3.3, but written with basic Windows batch scripts and a shell script for MSYS/MINGW32 support. I use bash and command line shell tools from msysgit, based on MSYS/MINGW32, to do most of my python development on Windows.

pywin supports several useful features defined in PEP 397, such as command line conventions and hash bang #! python version headers in source files. While pywin lacks some of py.exe’s features, it has the basics and a few extras of its own.


  • Windows >= XP for command prompt support
  • Windows >= Vista for MSYS/MINGW support (requires mklink for symbolic links)
  • At least one installation of python 2.5 up to 3.3 (though it’s not useful without at least two)
  • easy_install, pip, or git


  • Make sure the main python installation you want pywin to live under is in the PATH.
  • With multiple python installations, it’s recommended to have only the main and Scripts directories from one installation in your PATH. For example, C:\Python27;C:\Python27\Scripts.


easy_install pywin


pip install pywin

from source

git clone git://
cd pywin
python install

Getting Started

# Assuming pywin was installed with Python27


    HKEY_CURRENT_USER\Software\Classes python keys created successfully.

    .py files will launch with "C:\Python27\pywin.bat"

C:\>pywin genlaunchers

    Generating launchers...

    C:\Python27\python2.7.bat -> C:\Python27\python.exe
    C:\Python27\python2.6.bat -> C:\Python26\python.exe
    C:\Python27\python2.5.bat -> C:\Python25\python.exe
    C:\Python27\python3.0.bat -> C:\Python30\python.exe
    C:\Python27\python3.1.bat -> C:\Python31\python.exe
    C:\Python27\python3.2.bat -> C:\Python32\python.exe
    C:\Python27\python3.3.bat -> C:\Python33\python.exe

C:\>pywin               # launch first python found in PATH

C:\>pywin -2.7          # launch python 2.7

C:\>pywin setdefault 3.3

    Setting default python for active session to: 3.3
    C:\Python33;C:\Python33\Scripts -- now at front of PATH

# Create a test file with a specified python version in the header
C:\>echo #! /usr/bin/python2.7 >
C:\>echo import sys;print("\n  %s"%sys.exec_prefix) >>


C:\>pywin -3.2  # launch with python 3.2



pywin and its associated scripts are installed in the main directory of the active python version (e.g. C:27). There’s no need to install it under more than one version of python (if you do, you’ll have to run pywin genlaunchers for each version you install it under). Make sure that this main python directory is always on the path. Alternatively you can move the included scripts to another directory in your path.

Auto-generate version-specific launchers

pywin can create individual launch scripts to directly access core python installations (e.g. python2.7). These can be called directly with or without arguments from the Windows command prompt and MSYS/MINGW bash prompt. To use this feature, call

pywin genlaunchers

Launchers are created for all machine-wide and user-specific python installations found in the Windows registry. Windows batch files will be added to the directory where pywin is located. MSYS/MINGW32 relies on Windows links created programmatically with mklink, which is why you must have Windows >= Vista installed to make use of this project.

Launch a specific python version using pywin

pywin -2.7  # launch python 2.7
pywin -3.2  # launch with python 3.2

Automatically invoke the right python with a script header

Add a directive to the first or second line of a source file to have the correct interpreter called. Currently this only supports python launchers created by the pywin genlaunchers command. To use this feature, you must associate the .py extension with pywin.bat using the included pyassoc utility.



NOTE: pywin commands work from both Windows command line and MSYS/MINGW32 shell.


pywin genlaunchers

Search for python installations and create batch files in the same directory where pywin is installed.

Note if you’re using MSYS/MINGW32 this must be run again in the MSYS/MINGW32 shell, and you must have Windows >= Vista.


pywin setdefault <version>

Set the default python to <major>.<minor> version. Adds the right python home directory and its associated Scripts directory to the front of PATH. Removes any other existing reference to a python Scripts directory in PATH.


# Existing PATH: C:\Windows\System32;C:\Windows;C:\Python27;C:\Python27\Scripts

pywin setdefault 3.3

# New PATH: C:\Python33;C:\Python33\Scripts;C:\Windows\System32;C:\Windows;C:\Python27;
# C:\Python27 is preserved so that pywin can be found.

pywin setdefault is only active for the current cmd.exe (or MSYS/MINGW32 shell) session. If you want to change the default python permanently, you need to change your system or user PATH and make sure pywin is installed for that python version.

When calling this from MSYS/MINGW32, enter a dot first so the changes to $PATH propagate to your active shell. E.g. . pywin setdefault 3.3

launch with version and/or source

pywin [-<version>] [<source file>]

Launch either a specific <major>.<minor> version of python, or a source file, or both. Note that specifying a version of python on the command line will override any version in the header of the source file.


# launch python 2.7
pywin -2.7

# launch with python 3.2
pywin -3.2

# launch according to Version Search Order below

Version Search Order

pywin will launch the first version of python found among:

  1. Any version specified after a #! in the first 2 lines of the source. The interpreter will be invoked with any additional parameters.


    #! python3.3
    #! /usr/bin/python2.7 -v
  2. If the environment variable VIRTUAL_ENV is set, use that virtualenv’s python.exe.

  3. If the environment variable PYTHONHOME is set, use its python.exe.

  4. If none of the above, fall back to the first python.exe found on the path.


pyassoc [original] [all_users]

With no arguments, pyassoc will register the .py extension to run with %pyhome%\pywin.bat. This change is made in the registry to HKEY_CURRENT_USER, so that when .py files are invoked, any machine-wide setting is overridden.

Note that registry settings have no effect on launch .py files under MSYS/MINGW32.


  • original - restore .py registry settings to launch with %pyhome%\python.exe
  • all_users - if administrator, apply changes to HKEY_LOCAL_MACHINE and remove any HKEY_CURRENT_USER python keys. Note that users can override this with their own HKEY_CURRENT_USER values.


The variable %pyhome% used by pyassoc is set in this manner:

  1. If the environment variable PYTHONHOME is set, use it.
  2. If the environment variable DEFAULTPYTHON is set, use it. This is set when you call pywin setdefault <version>, but only lasts for the current session.
  3. The path the pyassoc.bat script is in.

Project details

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Source Distribution (25.4 kB view hashes)

Uploaded source

Supported by

AWS AWS Cloud computing Datadog Datadog Monitoring Facebook / Instagram Facebook / Instagram PSF Sponsor Fastly Fastly CDN Google Google Object Storage and Download Analytics Huawei Huawei PSF Sponsor Microsoft Microsoft PSF Sponsor NVIDIA NVIDIA PSF Sponsor Pingdom Pingdom Monitoring Salesforce Salesforce PSF Sponsor Sentry Sentry Error logging StatusPage StatusPage Status page