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Is it possible to install 2 versions of Python on Windows 7 and if so do I just need to run the separate installers? (and all will work well if I do, without any configuration?)

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up vote 3 down vote accepted

Yes. I suggest installing the version you will use the most last, because the installer adds Python to your system path adds registry entries for *.py files. These registry entries set the default "Open" action and add an "Edit with IDLE" context menu.

To use a specific version of Python, simply use the full path to the executable. And/or set the appropriate environment variables (%PATH% and %PYTHONPATH%) properly. This can be done at a Windows-wide level, then later over-ridden by a specific CMD console.


Update:

I just installed three versions of Python (2.5, 2.7, then 2.6) on Windows 7. I wanted to be able to specify which version of Python to use for "Open with IDLE", so I added some registry keys under: HKEY_CLASSES_ROOT\Python.File\shell\ in order to get two context menu items (Edit with IDLE 2.6 and Edit with IDLE 2.7):

  1. I cloned the existing Edit with IDLE key to create a new Edit with IDLE 2.7 key.
  2. Then I modified the string under the command key to use Python 2.7:
    "C:\Python27\pythonw.exe" "C:\Python27\Lib\idlelib\idle.pyw" -n -e "%1"
  3. Finally, I renamed the existing Edit with IDLE to Edit with IDLE 2.6
  4. I could have added another context menu item for Python 2.5, but I only plan to use 2.5 infrequently for Google Apps Engine.
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I found that the formal way to do this is as follows:

Just install two (or more, using their installers) versions of Python on Windows 7 (for me work with 3.3 and 2.7).

Follow the instuctions below, changing the parameters for your needs.

Create the following environment variable (to default on double click):

Name:  PY_PYTHON
Value: 3

To launch a script in a particular interpreter, add the following shebang (beginning of script):

#! python2

To execute a script using a specific interpreter, use the following prompt command:

> py -2 MyScript.py

To launch a specific interpreter:

> py -2

To launch the default interpreter (defined by the PY_PYTHON variable):

> py

Resources

Documentation: Using Python on Windows

PEP 397 - Python launcher for Windows

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Yes, no problem. I have it on my Windows 7 64 bit machine - I think i have Python 2.5 and 2.7 - each one was installed with other software - I think that one with Scidavis and second with Quantum GIS. Both programs are working OK. ;-)

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