Windows insists associating .py files with the wrong version of Python

Question

I have both Python 2.7 and Python 3.3 installed on my machine (I'm on Windows 8).

I would like .py files to be opened with Python 3.3 by default. The only Python path in the PATH environment variable is the 3.3 one. Still, when opening .py files I see they're being interpreted by Python 2.7, even when I explicitly open them with the Python 3.3 exe ("Open with" and choosing the 3.3 exe). I've also tried changing the Python.exe version using "Set Associations" in Windows' control panel. I'm not sure it has changed anything. No matter what I do, the output of the following program is 2.7.3:

import sys
print(sys.version)

How do I force Windows 8 to open .py files with Python 3.3?

Answer 1

It seems that windows is not checking the whole path of the executable! Try to rename the python.exe of version 2 (respectively 3) to some temp name. Then associate with this name. And change everything back.

FYI you could check the file association with:

C:\Users\shadowed>assoc .py
.py=Python.File

C:\Users\shadowed>ftype Python.File
Python.File="C:\Python27\python.exe" "%1" %*

Answer 2

Changing the shebang (#! python3) may help you, but you will have a problem: if your python script has parameters, they will be cut off when you run command

somepythonfile.py your_parameters

You will get py.exe running with just "somepythonfile.py" and NO parameters, believe me.

The method which worked for me is next: run the app http://www.nirsoft.net/utils/file_types_manager.html - this is a file association manager. Fix the association for python files to be

"C:\Windows\py.exe" "%1" %*

instead of

"C:\Windows\py.exe" "%1"

Or, alternatively, set

"C:\Python34\pythonw.exe" "%1" %*

explicitly - to match the desired version and omit the shebang line.

Answer 3

Try to add #!python3 to the very first line. Python 3.3 introduced Python Launcher for Windows that associates .py with c:\windows\py.exe. It launches the highest Python 2 by default.See https://stackoverflow.com/a/17245543/1346705

Answer 4

If you want to change the IDLE used when right clicking you can go into the registry and find the key:

HKEY_CLASSES_ROOT\Python.File\shell\Edit with IDLE\command

You should see something like:

"C:\Python27\pythonw.exe" "C:\Python27\Lib\idlelib\idle.pyw" -e "%1"

Change all the 27 to 33 if you installed your pythons in the default area. If not just change the path to where your 3.3 implementation is stored.

To change the default command line python you should do the same with the path in your PATH environment variable.

Answer 5

Have you tried uninstalling Python 2.7 temporarily? That might fix the file association. I am uncertain, as I am not familiar with Windows 8 beyond what little I learned of it when I tried it on someone else's computer. I'm not even sure it would work on Windows 7, but it is worth a shot if you ask me.

I also recommend using the tag for the specific version of Windows you are using, rather than the standard "windows" tag. In this case, I might use both, since file associations don't change much between versions of Windows. At least use the correct tag (windows-8), at any rate. Then you will get more answers from people looking for that tag.