My MacBook came preinstalled with Python 2.7.16, and I downloaded Python 3.8.5. To my understanding, the operating system needs Python 2.x so I did not uninstall it.
Eclipse (using Pydev) is the IDE I'm using.
I set up two interpreters, one for python and the other python3.
I set up one project for each interpreter to make sure I set them up correctly.
The script is:
import sys
print(sys.version)
When I run it with the python interpreter, I correctly get version 2.7.16.
When I run it with the python3 interpreter, I instead get 3.8.2.
Running python -V yields ``Python 2.7.16. Running python3 -VyieldsPython 3.8.5```.
Why does the interpreter return one version and the terminal another?
I'm at a loss for how to troubleshoot or fix this, or if it is a non-issue.
To clarify, you get the 2.7.16 and 3.8.2 versions when running your program from within Eclipse. The python -V is clearly from the command line. The interpretation is that your Eclipse environment came with its own python interpreter which happened to be 3.8.2. Have you tried running your script from the command line with python3 path/to/your/script.py? This probably gives 3.8.5. I don't see a real problem here in most cases you do not care whether you have python 3.8.2 or 3.8.5.
The "biggest" issue is a cosmetic one that you have two python3 installations which is a bit of a waste. When using additional libraries, you may find that you have to install them in your Eclipse environment and in your command line if you want to use your scripts in both environments which would be a bit tedious. If this does turn out to be a problem, check in Eclipse whether there is any way to change your python3 configuration to use the interpreter used by the command line (sorry cannot be more specific, it's a long time that I used Eclipse).
This question already has answers here:
How to run multiple Python versions on Windows
(22 answers)
Closed 6 years ago.
How can I configure windows command dialog to run different python versions in it? For example when I type python2 it runs python 2.7 and when I type python3 it runs python 3.3? I know how to configure environment variables for one version but two? I mean something like Linux terminal.
I also met the case to use both python2 and python3 on my Windows machine. Here's how i resolved it:
download python2x and python3x, installed them.
add C:\Python35;C:\Python35\Scripts;C:\Python27;C:\Python27\Scripts to environment variable PATH.
Go to C:\Python35 to rename python.exe to python3.exe, also to C:\Python27, rename python.exe to python2.exe.
restart your command window.
type python2 scriptname.py, or python3 scriptname.py in command line to switch the version you like.
Python 3.3 introduces Python Launcher for Windows that is installed into c:\Windows\ as py.exe and pyw.exe by the installer. The installer also creates associations with .py and .pyw. Then add #!python3 or #!python2 as the first lline. No need to add anything to the PATH environment variable.
Update: Just install Python 3.3 from the official python.org/download. It will add also the launcher. Then add the first line to your script that has the .py extension. Then you can launch the script by simply typing the scriptname.py on the cmd line, od more explicitly by py scriptname.py, and also by double clicking on the scipt icon.
The py.exe looks for C:\PythonXX\python.exe where XX is related to the installed versions of Python at the computer. Say, you have Python 2.7.6 installed into C:\Python27, and Python 3.3.3 installed into C:\Python33. The first line in the script will be used by the Python launcher to choose one of the installed versions. The default (i.e. without telling the version explicitly) is to use the highest version of Python 2 that is available on the computer.
I would suggest using the Python Launcher for Windows utility that was introduced into Python 3.3. You can manually download and install it directly from the author's website for use with earlier versions of Python 2 and 3.
Regardless of how you obtain it, after installation it will have associated itself with all the standard Python file extensions (i.e. .py, .pyw, .pyc, and .pyo files). You'll not only be able to explicitly control which version is used at the command-prompt, but also on a script-by-script basis by adding Linux/Unix-y shebang #!/usr/bin/env pythonX comments at the beginning of your Python scripts.
I installed python 3.2 and later installed python 2.7. Somehow the IDLE, which I open it by right-click on python file -> Edit with IDLE, are using python 2.7 instead of python 3.2.
It seems that python 2.7 was set as default with IDLE. Even if I changed the PATH environment variable in windows advance setting back to python 3.2, the default python shell is still 2.7. I am sure that there was no more python 2.7 in the path.
Later I have to uninstall python 2.7 and reinstall python 3.2.
The IDLE context menu plug-in is registered when you install Python and points to the version of IDLE supplied with the Python installed. (IDLE itself has significant code changes between Python 2 and 3 because it's written in Python and the language changed a lot.) To change it, simply re-install the version of Python you wish the IDLE context menu to invoke.
I'm new to python. I've installed both Python 3.2.2 for x64 and Python 2.7 for x86 on my 64-bit windows machine. I've got some python code that are coded for python 2.x versions. But every time I try to run them by double clicking it is interpreted by python 3.x.
How do I force them to use python version 2.7, may be using some directives or using a BATCH script?
Going forward, the solution is to upgrade Python 3.2 to 3.3 or later and use the Python Launcher for Windows.
At the top of each Python 3 program, include the following line:
#!/usr/bin/env python3
At the top of each Python 2 program, include the following line:
#!/usr/bin/env python2
The #! part, called a shebang, indicates to Python Launcher which version of Python is desired. (It also indicates to UNIX that a program should be run with a particular interpreter instead of the shell.) The /usr/bin/env part helps locate the Python interpreter on your PATH when you run a program on UNIX. If you don't plan on using anything but Windows, you can leave it out:
#! python3
[or]
#! python2
You could, e.g., associate the file extension .py2 with Python 2.7 and rename the main file (assuming you regard Python 3.2 as your default version).
open a command line window, and use "c:\python27\python.exe" yourscript.py (or whatever path your python 2.7 appears to be installed in).
of course, you can put that line into a batch file and execute the batch.
also, you can put a shortcut to c:\python27\python.exe on your desktop and drop your script onto that shortcut every time you want to run it.
try editing PATH environment variable, use python 2.7 path and delete python 3.2.2
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.
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
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)
I have multiple versions in windows.
I just change the exe name of the version I'm not defaulting to.
python.exe --> python26.exe
pythonw.exe --> 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
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
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.
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! ;-)
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. :)
Starting version 3.3 Windows version has Python launcher, please take a look at section 3.4. Python Launcher for Windows
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.
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
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.
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.
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.
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.
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.
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=<path_python_2.7>
PYTHON_HOME_3.8.1=<path_python_3.8.1>
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.
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.
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.
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?