Can I install Python 3.x and 2.x on the same Windows computer?

Question

The official solution for coexistence seems to be the Python Launcher for Windows, PEP 397 which was included in Python 3.3.0. Installing the release dumps py.exe and pyw.exe launchers into %SYSTEMROOT% (C:\Windows) which is then associated with py and pyw scripts, respectively.

In order to use the new launcher (without manually setting up your own associations to it), leave the "Register Extensions" option enabled. I'm not quite sure why, but on my machine it left Py 2.7 as the "default" (of the launcher).

Running scripts by calling them directly from the command line will route them through the launcher and parse the shebang (if it exists). You can also explicitly call the launcher and use switches: py -3 mypy2script.py.

All manner of shebangs seem to work

• #!C:\Python33\python.exe
• #!python3
• #!/usr/bin/env python3

as well as wanton abuses

• #! notepad.exe

Here's my setup:

1. Install both Python 2.7 and 3.4 with the windows installers.
2. Go to C:\Python34 (the default install path) and change python.exe to python3.exe
3. Edit your environment variables to include C:\Python27\;C:\Python27\Scripts\;C:\Python34\;C:\Python34\Scripts\;

Now in command line you can use python for 2.7 and python3 for 3.4.

From version 3.3 Python introduced Launcher for Windows utility https://docs.python.org/3/using/windows.html#python-launcher-for-windows.

So to be able to use multiple versions of Python:

1. install Python 2.x (x is any version you need)
2. install Python 3.x (x is any version you need also you have to have one version 3.x >= 3.3)
3. open Command Prompt
4. type py -2.x to launch Python 2.x
5. type py -3.x to launch Python 3.x

You can have both installed.

You should write this in front of your script:

#!/bin/env python2.7

or, eventually...

#!/bin/env python3.6

Update

My solution works perfectly with Unix, after a quick search on Google, here is the Windows solution:

#!c:/Python/python3_6.exe -u

Same thing: in front of your script.

I'm using 2.5, 2.6, and 3.0 from the shell with one line batch scripts of the form:

:: The @ symbol at the start turns off the prompt from displaying the command.
:: The % represents an argument, while the * means all of them.
@c:\programs\pythonX.Y\python.exe %*

Name them pythonX.Y.bat and put them somewhere in your PATH. Copy the file for the preferred minor version (i.e. the latest) to pythonX.bat. (E.g. copy python2.6.bat python2.bat.) Then you can use python2 file.py from anywhere.

However, this doesn't help or even affect the Windows file association situation. For that you'll need a launcher program that reads the #! line, and then associate that with .py and .pyw files.