Using VirtualEnv with multiple Python versions on windows
python, virtualenv
Solution
Better:
py -3.4 -m venv c:\path\to\wherever\you\want\it
If you don't have the `py.exe` launcher (but it should be installed) you can replace `py -3.4` with `c:\Python34\python.exe` (assuming the default location)
This does require the selected Python runtime version to be installed on the machine. You can install any version via the Microsoft Store or by downloading its installer from the website.
This works because of the handy-dandy, Windows-versioningest, super nice runtime picker `py.exe`
By default, `py.exe` will be present on a Windows install (I think it comes with 2.7, I know it does with 3+). When you run `py` then it will search for some environment variables or you can override that with a specific verison number (in your case `-2.7`or `-3.4`) You can leave off the `.4` and it will choose the "biggest" minor version number.
You can also use it to run Python scripts. If you put a hash-bang line at the top of your script `#!python3` and call it `py myscript.py` then it will pick the correct version of Python to start with, by searching the first line of the script and searching for a version number.
This is cool, because you can put something like `#!/usr/bin/env python3.4` in the top of your script and run it on Windows with `py`, or on linux by doing
$ chmod +x myscript.py
$ ./myscript.py
Pretty useful.
Problem
I have python 2.7.6 and 3.4.0 on my machine. The 2.7 version is on my path. I would like to set up a virtualenv using 3.4. There are many postings on SO and elsewhere that suggest I do the following from a command prompt: ``` virtualenv -p c:\python34 myvirtualenv ``` but this does not work for me. The console session has administrator privilege and UAC is off, however I get a permissions problem: ``` F:\virtualenv>virtualenv -p c:\python34 myenv Running virtualenv with interpreter c:\python34 Traceback (most recent call last): File "c:\python27\scripts\virtualenv-script.py", line 9, in <module> load_entry_point('virtualenv==1.11', 'console_scripts', 'virtualenv')() File "C:\Python27\lib\site-packages\virtualenv.py", line 779, in main popen = subprocess.Popen([interpreter, file] + sys.argv[1:], env=env) File "C:\Python27\lib\subprocess.py", line 709, in __init__ errread, errwrite) File "C:\Python27\lib\subprocess.py", line 957, in _execute_child startupinfo) WindowsError: [Error 5] Access is denied ``` I have also tried it specifically pointing to the 3.4 version of virtualenv, but without changing the path it ends up executing a mixed bag of 2.7 and 3.4 python files. The only way I could find to set up my virtual environment is to change my path to 3.4, run virtualenv then reset my path to 2.7, which defeats the point of the python switch on virtualenv. Thanks