How to install both Python 2 x and Python 3 x in Windows

Question

I do most of my programming in Python 3 x on Windows 7  but now I need to use the Python Imaging Library  PIL   ImageMagick  and wxPython  all of which require Python 2 x   Can I have both Python 2 x and Python 3 x installed in Windows 7  When I run a script  how would I  choose  which version of Python should run it  Will the aforementioned programs be able to handle multiple versions of Python installed at once  I have searched for hours and hours for how to do this to no avail   Thanks

User · Answer

Install the one you use most  3 3 in my case  over the top of the other  That ll force IDLE to use the one you want   Alternatively  from the python3 3 README    Installing multiple versions  On Unix and Mac systems if you intend to install multiple versions of Python using the same installation prefix  --prefix argument to the configure script  you must take care that your primary python executable is not overwritten by the installation of a different version   All files and directories installed using  make altinstall  contain the major and minor version and can thus live side-by-side    make install  also creates   prefix  bin python3 which refers to   prefix  bin pythonX Y   If you intend to install multiple versions using the same prefix you must decide which version  if any  is your  primary  version  Install that version using  make install    Install all other versions using  make altinstall    For example  if you want to install Python 2 6  2 7 and 3 3 with 2 7 being the primary version  you would execute  make install  in your 2 7 build directory and  make altinstall  in the others

User · Answer

Starting version 3 3 Windows version has Python launcher  please take a look at section 3 4  Python Launcher for Windows

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Only Works if your running your code in your Python IDE  I have both Python 2 7 and Python 3 3 installed on my windows operating system  If I try to launch a file  it will usually open up on the python 2 7 IDE  How I solved this issue  was when I choose to run my code on python 3 3  I open up python 3 3 IDLE Python GUI   select file  open my file with the IDLE and save it  Then when I run my code  it runs to the IDLE that I currently opened it with  It works vice versa with 2 7

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I use a simple solution to switch from a version to another version of python  you can install all version you want  All you have to do is creating some variable environment  In my case  I have installed python 2 7 and python 3 8 1  so I have created this environment variables   PYTHON HOME 2 7  lt path python 2 7 gt  PYTHON HOME 3 8 1  lt path python 3 8 1 gt  PYTHON HOME  PYTHON HOME 2 7   then in my PATH environment variable I put only  PYTHON HOME  and  PYTHON HOME  Scripts  In the example above I m using the version 2 7  when I want to switch to the other version I have only to set the PYTHON HOME  PYTHON HOME 3 8 1   I use this method to switch quickly from a version to another also for JAVA  MAVEN  GRADLE ANT  and so on

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What I did was download both 2 7 6 and 3 3 4  Python 3 3 4 has the option to add the path to it in the environment variable so that was done  So basically I just manually added Python 2 7 6   How to      Start   in the search type in environment select  Edit environment variables to your account 1 Scroll down to Path  select path  click edit  Add C  Python27  so you should have paths to both versions of Python there  but if you don t this you can easily edit it so that you do      C  Python27 C  Python33  Navigate to the Python27 folder in C   and rename a copy of python exe to python2 exe Navigate to the Python34 folder in C   and rename a copy of python exe to python3 exe Test  open up commmand prompt and type python2     BOOM  Python 2 7 6  exit out  Test  open up commmand prompt and type python3     BOOM  Python 3 4 3  exit out    Note   so as not to break pip commands in step 4 and 5  keep copy of python exe in the same directory as the renamed file

User · Answer

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    gt  py -2 MyScript py   To launch a specific interpreter    gt  py -2   To launch the default interpreter  defined by the PY PYTHON variable     gt  py   Resources  Documentation  Using Python on Windows  PEP 397 - Python launcher for Windows

User · Answer

Check your system environment variables after installing Python  python 3 s directories should be first in your PATH variable  then python 2   Whichever path variable matches first is the one Windows uses   As always py -2 will launch python2 in this scenario

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I actually just thought of an interesting solution  While Windows will not allow you to easily alias programs  you can instead create renamed batch files that will call the current program   Instead of renaming the executable which will break a lot of thing including pip  create the file python2 bat in the same directory as the python2 exe  Then add the following line     dp0python      What does this archaic syntax mean  Well  it s a batch script   Windows version of bash     dp0 gets the current directory and    will just pass all the arguments to python that were passed to the script    Repeat for python3 bat  You can also do the same for pip and other utilities  just replace the word python in the file with pip or whathever the filename  The alias will be whatever the file is named   Best of all  when added to the PATH  Windows ignores the extension so running  python3   Will launch the python3 version and and the command python2 will launch the python2 version   BTW  this is the same technique Spyder uses to add itself to the path on Windows

User · Answer

Here s what you can do   Install cmder  Open and use Cmder as you would with you cmd terminal  Use the command alias to create command aliases   I did the following   alias python2   c  python27 python exe alias python3   c  python34 python exe   And that s it   -

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I just had to install them  Then I used the free  and portable  soft at http   defaultprogramseditor com  under  File type settings   Context menu  search  py   chose  py file and added an  open  command for the 2 IDLE by copying the existant command named  open with IDLE  changing names to IDLE 3 4 1 2 7 8  and remplacing the files numbers of their respective versions in the program path  Now I have just to right click the  py file and chose which IDLE I want to use  Can do the same with direct interpreters if you prefer

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I have multiple versions in windows  I just change the exe name of the version I m not defaulting to   python exe -- gt  python26 exe pythonw exe -- gt  pythonw26 exe  As for package installers  most exe installers allow you to choose the python install to add the package too  For manual installation check out the --prefix option to define where the package should be installed  http   docs python org install index html alternate-installation-windows-the-prefix-scheme

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I did this in three steps by following the instructions here  This is all taken directly from here  http   ipython readthedocs io en stable install kernel install html  I m currently running Python 2 x on Windows 8 and have Anaconda 4 2 13 installed    1  First install the latest version of python   conda create -n python3 python 3 ipykernel   2  Next activate python3  activate python3   3  Install the kernel   python -m ipykernel install --user   If you have Python 3 installed and want to install 2  switch the 2 and the 3 above  When you open a new notebook  you can now choose between Python 2 or 3

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I have installed both python 2 7 13 and python 3 6 1 on windows 10pro and I was getting the same  Fatal error  when I tried pip2 or pip3    What I did to correct this was to go to the location of python exe for python 2 and python 3 files and create a copy of each  I then renamed each copy to python2 exe and python3 exe depending on the python version in the installation folder  I therefore had in each python installation folder both a python exe file and a python2 exe or python3 exe depending on the python version    This resolved my problem when I typed either pip2 or pip3

User · Answer

To install and run any version of Python in the same system follow my guide below      For example say you want to install Python 2 x and Python 3 x on the same Windows system     Install both of their binary releases anywhere you want     When prompted do not register their file extensions and  do not add them automatically to the PATH environment variable   Running simply the command python the executable that is first met in PATH will be chosen for launch  In other words  add the Python directories manually  The one you add first will be selected when you type python  Consecutive python programs  increasing order that their directories are placed in PATH  will be chosen like so     py -2 for the second python  py -3 for the third python etc     No matter the order of  pythons  you can     run Python 2 x scripts using the command  py -2  Python 3 x functionality   ie  the first Python 2 x installation program found in your PATH will be selected   run Python 3 x scripts using the command  or py -3  ie  the first Python 3 x installation program found in your PATH will be selected        In my example I have Python 2 7 14 installed first and Python 3 5 3  This is how my PATH variable starts with    PATH C  Program Files Microsoft MPI Bin  C  Python27 C  Program Files Python 3 6 Scripts  C  Program Files Python 3 6  C  ProgramData Oracle Java javapath C  Program Files  x86  Common Files Intel Shared        Note that Python 2 7 is first and Python 3 5 second     So running python command will launch python 2 7  if Python 3 5 the same command would launch Python 3 5    Running py -2 launches Python 2 7  because it happens that the second Python is Python 3 5 which is incompatible with py -2    Running py -3 launches Python 3 5  because it s Python 3 x    If you had another python later in your path you would launch like so  py -4  This may change if when Python version 4 is released     Now py -4 or py -5 etc  on my system outputs  Requested Python version  4  not installed or Requested Python version  5  not installed etc    Hopefully this is clear enough

User · Answer

If you use Anaconda Python  you can easily install various environments   Say you had Anaconda Python 2 7 installed and you wanted a python 3 4 environment   conda create -n py34 python 3 4 anaconda   Then to activate the environment   activate py34   And to deactive   deactivate py34    With Linux  you should use source activate py34    Links   Download Anaconda Python  Instructions for environments

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I have encountered that problem myself and I made my launchers in a  bat so you could choose the version you want to launch    The only problem is your  py must be in the python folder  but anyway here is the code   For Python2   echo off title Python2 Launcher by KinDa cls echo Type the exact version of Python you use  eg  23  24  25  26  set p version  cls echo Type the file you want to launch without  py  eg  hello world  calculator  set p launch  path    PATH  C  Python version  cd C  Python version  python  launch  py pause   For Python3   echo off title Python3 Launcher by KinDa cls echo Type the exact version of Python you use  eg  31  32  33  34  set p version  cls echo Type the file you want to launch without  py  eg  hello world  calculator  set p launch  cls set path    PATH  C  Python version  cd C  Python version  python  launch  py pause   Save them as  bat and follow the instructions inside

User · Answer

What I have done on my own windows computer where I have Python 2 7 and Python 3 4 installed is I wrote a simple  bat file in the same directory as my Python exe files  They look something like   cmd  k  c  python27 python exe       The    allows you to add arguments  Python files  afterwards  I believe  k keeps the prompt open after it finishes running the script  Then I save that as python27 bat Then I go to my Python 3 directory and make a bat file there  Now in my command line I can write  Python27 helloworld py   Or  Python34 helloworld py   And they will run in their respective versions of Python  Make sure that c  python27 and c  python34 are in your environment variables   I got my answer from here

User · Answer

You can install multiple versions of Python one machine  and during setup  you can choose to have one of them associate itself with Python file extensions  If you install modules  there will be different setup packages for different versions  or you can choose which version you want to target  Since they generally install themselves into the site-packages directory of the interpreter version  there shouldn t be any conflicts  but I haven t tested this   To choose which version of python  you would have to manually specify the path to the interpreter if it is not the default one  As far as I know  they would share the same PATH and PYTHONPATH variables  which may be a problem   Note  I run Windows XP  I have no idea if any of this changes for other versions  but I don t see any reason that it would

User · Answer

If you can t get anything else to work  open an interpreter in whichever version you choose  I prefer using iPython  and   import subprocess  subprocess call  python script py -flags     This uses whichever python version you are currently operating under  Works fine for a single script  but will quickly get out of hand if there are lots of scripts you run  in which case you can always make a batch file with all of these calls inside  Not the most elegant answer  but it works   Is there a way to make aliases for different python version a la Linux

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