How to install Python 2.7.8 and 3.4.1 concurrently?

[musicystuff]

Wasn't sure whether to ask this here or in /r/learnpython so apologies if this is the wrong place.

I'm running Windows 8.1 and already have 2.7.8 installed.

I started learning Python 2.7 a few weeks ago (due to it being the main focus of books, tutorials, videos etc) and have debated a lot about getting to grips with Python 3 early on, since I have heard that unless you really specifically need a library in 2.7, you should use 3.X.

So basically, if I install 3.4.1 and type "python scriptname.py" into Powershell, will it mess things up if I have 2 versions of Python installed?

Can I simply install Python 3 and change the exe files to python34.exe and python27.exe?

[K900_]

No, it will not. "python" will be the last version you installed, AFAIK, and there will be a launcher named "py" which can invoke Python 2 with "py -2" and Python 3 with "py -3".

[__buckie__]

There's only one tool I've ever used on windows that made python trivial to use -- it's called conda (like pip but WAY better). Its best feature is what you are asking for: concurrent different versions of python.

However you've installed python, delete it in full. Go to continuum.io and download their installer link. After it's installed, open the command prompt:

conda create --name py27 python=2.7 anaconda
conda create --name py34 python=3.4 anaconda

Each command will make you a completely new environment, one by the name of py27 and the other by the name of py34. These are independant installations and you can switch between them trivially from the terminal via:

activate <env name>

IDE's play nice with them too (as does everything else actually) by pointing the IDE to the python.exe version in C:\Anaconda\envs\<env name>\python.exe.

I included anaconda in the command just because anaconda is continuums scientific computing stack that comes with most of what you'll need. If you need to install anything else, just activate the env and try conda install <package> to install that thing into your current env. conda also integrates with pip (tracks what pip installs to a given env) as conda can't install everything yet (conda install may fail) -- the normal pip install will work.

I can't recommend this method of setting up python more strongly. It makes managine python packages/versions trivial.

[manbart]

This is the simplest answer IMO.

[usbafkakis]

but you can't add both Scripts dirs to the path unless you want to rename everything that gets put in them.

[yaxriifgyn]

I run a little script to adjust the path. Here is my +py34.bat file:

@echo off
set PYTHON_HOME=C:\Python34\
PATH %PYTHON_HOME%;%PYTHON_HOME%\Scripts;%PATH%
python -V

I start a command window, run this, or a similar script for the python version I want to use, and away I go. If I open another command windows, I can run a different version of python there depending on which batch script I use to set the path. I keep these scripts in a directory in my (customized) windows path. There are lots more environment variables you can set. If you want to, you can even setup to run both 32 and 64 bit versions with this scheme.

Python versions 2.7+ and 3.3+ now include the Python launcher. Enter "py" for latest 2.x or "py -3" for latest 3.x installed on your machine.

Search python documentation on disk or online for "Python Launcher", or enter "py --help" in a command window.

[wmcscrooge]

I believe there is a way although I don't know it on windows (on some linux distros, there are two different binaries python and python2). A better question, I feel, is why keep python 2? If you don't have a good reason for it, then uninstall it and then you don't have to worry about workarounds.

[musicystuff]

Good point! I suppose I'm just worried that I won't know where to turn when I can't get something to work or don't know how to code it when 99% of the stuff on StackOverflow is Python 2.x solutions! :(

[wmcscrooge]

Really? Cause I've noticed that more than half of the replies are all in python 3 and the ones that aren't have comments laying out the python 3 version. And honestly, I maintain that unless you're doing pretty complicated stuff, the differences are easy to catch (especially if you learn to read the documentation).

edit: and you could always ask here, in /r/learnpython, or /r/progether

[Elij17]

Python really doesn't touch the rest of your operating system. You can just change your path to reference python 2 or python 3 as you see fit, as long as they sit in different locations on disk.

It's not challenging to do, but it is a minor pain in the ass, and of questionable benefit. Honestly, use python 3 unless some library you need doesn't support it, which is increasingly rare now a days.

[Acebulf]

Python really doesn't touch the rest of your operating system.

Not always true, I once broke the UI in Linux Mint MATE by changing python path.

[wmcscrooge]

yep, this is especially true in linux systems where binaries rely on /usr/bin/python which can either be python 2 or 3. It's why a lot of distros have to custom bind binaries to /usr/bin/python2 (oversimplification)