How to use Python 3.8 and 3.7 on Windows 10. I want to make two applications, but one requires 3.8 and another one 3.7.
So how to manage both versions in one Windows 10.
You should just install Python 3.7 and Python 3.8 and make sure that the Python Launcher for Windows is also installed (this is the default).
Then you could run your scripts using py -3.7 main.py or py -3.8 main.py to run main.py using Python versions 3.7 or 3.8, respectively.
Alternatively (even better actually), you could write the required Python version in the first line of your Python script:
#!/usr/bin/env python3.7
Note that this must be the first line of the script, otherwise it doesn't work. Now just running py main.py would automatically select the correct Python version to execute the script.
NB: If the script is executed in Linux it would also run with the correct Python version.
Using virtual environment you can install several python versions and more importantly you can install different modules version for each of those python revision (the main reason for running different python version is that some modules are not (yet) compatible with recent python releases).
You can check how to create/update and activate different virtual environment here.
Those env can use their own python version or share it, it is chosen at creation time (the python version you use when creating the env is the one that will be used any time you activate the env).
I installed Python 3.6 on Debian 9 with
nix-env -i python3-3.6.2
but now my python interpreter has changed from the default Python 2.7 to this Python 3.6.2:
which python
/home/user/.nix-profile/bin/python
and this breaks a lot of stuff. How can I install Python 3.6 without replacing the standard Python interpreter?
That's right, python3 on Nixpkgs provides python executable. The root cause of this is that user installed programs hide system-wide programs (see your PATH envvar).
You should install python2 too, and solve the priority override for python executable.
But you may be interested in nix-shell -p python3 instead, which creates temporal environment with python3 and leaves python 2 elsewhere.
Just curious, is there a particular reason why Python 3.x is not installed on Windows to run default with the command line "python3", like it does on Mac OSX and Linux? Is there some kind of way to configure Python so that it runs like this? Thanks.
EDIT: Just to add, the reason I am asking is because I have both the Python 2 and 3 interpreter installed on my computer, and so it is ambiguous, as both are run using the command "python".
the reason I am asking is because I have both the Python 2 and 3 interpreter installed on my computer, and so it is ambiguous, as both are run using the command "python".
To run Python 2 executable:
C:\> py -2
To run Python 3 executable:
C:\> py -3
where py is a Python launcher that is bundled with your Python 3 installation.
py recognizes the shebang (e.g., #!/usr/bin/env python3 causes Python 3 executable to be run), it respects virtualenv (if you run py without specifying the explicit python executable version) i.e., run:
C:\> py your_script.py
and the correct python version is used automatically -- you don't need to specify the Python version on the command-line explicitly.
is there a particular reason why Python 3.x is not installed on Windows to run default with the command line "python3", like it does on Mac OSX and Linux?
OSX and Linux have python executable installed by default as a rule and it refers to Python 2 version in most cases at the moment that is why you need a separate python3 name there.
There is no Python on Windows by default. And therefore any version that you've installed is just python (I guess). The recommended way to manage multiple python versions is to use the Python launcher.
Is there some kind of way to configure Python so that it runs like this?
If you want to type python3 some_script.py instead of py some_script.py or even just some_script (assuming .py is in %PATHEXT% and Python launcher is configured to run Python scripts (check assoc .py and ftype Python.File) -- the default) then create a bat-file e.g., python3.cmd and put it in %PATH%:
"C:\path to\Python 3.X\python.exe" %*
You likely missed the checkbox at the bottom of the installer.
Full documentation here: https://docs.python.org/3/using/windows.html
Then, I think you just run python, not python3 from the Command Prompt. The reason Unix systems have python3 is because python defaults to Python2.x in many systems.
You have to add the python bin folder to your path. You can do it manually but when you install python i remember you have an option to do that.
I work with multiple Python 2.x and 3.x distros on Windows. Some of them are "portable" - i.e. not recorded in the Windows registry, and therefore not accessible by the version-selector py.exe delivered with Python 3.3+. To save my sanity, I wrote SelectPython.bat which is available on bitbucket. It configures the PYTHONHOME, PYTHONPATH and PATH variables according to the target you give it (a relative or absolute path to the parent directory of python.exe). You can do so in a way that is sticky for the rest of your command-line session:
> SelectPython C:\Path\To\Desired\Version\Of\Python
> python
or transiently, i.e. to call a particular python command without otherwise affecting the environment of the shell you're calling it from:
> SelectPython C:\Path\To\Desired\Version\Of\Python python -c "import sys;print(sys.version)"
You may find it helpful.
I am trying to uninstall Python 3.2 and go back to 2.7, I do not have much experience with Python, and as I am learning now, it is becoming increasingly difficult to manage all of the work arounds needed to work with the newest version, and I require 2.7 for a college course.
I tried using the Windows 7 add/remove programs to uninstall Python 3.2 and 3.1, and then I downloaded and installed the 64 bit Python 2.7, but I was unable to open any of my already existing .py files with the executable in the Python27 folder.
When I click to open any .py file, I don't see any error messages but Windows asks what program to open the file with, and if I choose python.exe or pythonw.exe in C:\Python 27 I get a console Window appearing briefly and then closing. The "edit with IDLE" option in the context menu is gone, and if I try to edit with IdleX, I get another "what application to open with" window.
Instead of removing python 3.2, you can use both of python 2 and 3 in the same time. You just need to specify which version you want to use.
When in CMD, you can see the available versions installed on your windows. If it doesn't appear there, you need to install it.
py -0 # Prints out the versions you can use.
You can specify which python version you want to use.
For example in Windows 10, I use the code below for python 3.
py -3 fileName.py # runs using python 3
For python 2, you can use the code below after installing it.
py -2 fileName.py # Runs using python 2
Here is more information about installing more versions of Python in the same time.
How to install both Python 2.x and Python 3.x in Windows 7
Python 3.x is not backward compatible with Python 2.x, which was the purpose of the release. To clean up Python2.x without worrying about backward compatibility.
You can have as many python installations as you want on your computer, as they do not interact with each other. The python installations have it's own folder, with it's own idle, modules, launcher, ect.
You could install PyCharm or another Python IDE. It allows you to change which version of python you use to interpret your code. This will also identify syntax errors as you are writing and will notify you of them - in case you have code that works in 3.x but not 2.x.
Ecker00 is right, installing 2.7 in a separate directory gives you access to 2.7 while still having 3.x on your computer. You will have to re-install libraries with the Python27 folder's pip in order to use them in 2.7 though.
You can also change your python version using anaconda:
conda install python=3.5.0
or maybe
conda install python=2.7.8
or whatever you want.
Use the following steps to get it fixed.
//Check current Python pointer
ls -l python
//Check available Python versions
ls -l python*
//Unlink current python version
sudo unlink python
//Select required python version and lin to python command
sudo ln -s /usr/bin/python2.7 python
//Confirm change in pointer
ls -l python
I had two versions of Python installed on my machine (versions 2.6 and 2.5). I want to run 2.6 for one project and 2.5 for another.
How can I specify which I want to use?
I am working on Windows XP SP2.
Running a different copy of Python is as easy as starting the correct executable. You mention that you've started a python instance, from the command line, by simply typing python.
What this does under Windows, is to trawl the %PATH% environment variable, checking for an executable, either batch file (.bat), command file (.cmd) or some other executable to run (this is controlled by the PATHEXT environment variable), that matches the name given. When it finds the correct file to run the file is being run.
Now, if you've installed two python versions 2.5 and 2.6, the path will have both of their directories in it, something like PATH=c:\python\2.5;c:\python\2.6 but Windows will stop examining the path when it finds a match.
What you really need to do is to explicitly call one or both of the applications, such as c:\python\2.5\python.exe or c:\python\2.6\python.exe.
The other alternative is to create a shortcut to the respective python.exe calling one of them python25 and the other python26; you can then simply run python25 on your command line.
Adding two more solutions to the problem:
Use pylauncher (if you have Python 3.3 or newer there's no need to install it as it comes with Python already) and either add shebang lines to your scripts;
#! c:\[path to Python 2.5]\python.exe - for scripts you want to be run with Python 2.5
#! c:\[path to Python 2.6]\python.exe - for scripts you want to be run with Python 2.6
or instead of running python command run pylauncher command (py) specyfing which version of Python you want;
py -2.6 – version 2.6
py -2 – latest installed version 2.x
py -3.4 – version 3.4
py -3 – latest installed version 3.x
Install virtualenv and create two virtualenvs;
virtualenv -p c:\[path to Python 2.5]\python.exe [path where you want to have virtualenv using Python 2.5 created]\[name of virtualenv]
virtualenv -p c:\[path to Python 2.6]\python.exe [path where you want to have virtualenv using Python 2.6 created]\[name of virtualenv]
for example
virtualenv -p c:\python2.5\python.exe c:\venvs\2.5
virtualenv -p c:\python2.6\python.exe c:\venvs\2.6
then you can activate the first and work with Python 2.5 like this
c:\venvs\2.5\activate
and when you want to switch to Python 2.6 you do
deactivate
c:\venvs\2.6\activate
From Python 3.3 on, there is the official Python launcher for Windows (http://www.python.org/dev/peps/pep-0397/). Now, you can use the #!pythonX to determine the wanted version of the interpreter also on Windows. See more details in my another comment or read the PEP 397.
Summary: The py script.py launches the Python version stated in #! or Python 2 if #! is missing. The py -3 script.py launches the Python 3.
As per #alexander you can make a set of symbolic links like below. Put them somewhere which is included in your path so they can be easily invoked
> cd c:\bin
> mklink python25.exe c:\python25\python.exe
> mklink python26.exe c:\python26\python.exe
As long as c:\bin or where ever you placed them in is in your path you can now go
> python25
For example for 3.6 version type py -3.6.
If you have also 32bit and 64bit versions, you can just type py -3.6-64 or py -3.6-32.
install python
C:\Python27
C:\Python36
environment variable
PYTHON2_HOME: C:\Python27
PYTHON3_HOME: C:\Python36
Path: %PYTHON2_HOME%;%PYTHON2_HOME%\Scripts;%PYTHON3_HOME%;%PYTHON3_HOME%\Scripts;
file rename
C:\Python27\python.exe → C:\Python27\python2.exe
C:\Python36\python.exe → C:\Python36\python3.exe
pip
python2 -m pip install package
python3 -m pip install package
I strongly recommend the pyenv-win project.
Thanks to kirankotari's work, now we have a Windows version of pyenv.
One easy way for this is that you can use
py -3.8 -m pip install virtualenv here -3.8 goes with your [version number]
After installing the virtualenv, you can create the virtual environment of your application using
py -3.8 -m virtualenv [your env name]
then cd to venv, enter activate
This would activate the python version you like.
Just change the version number to use a different python version.
When you install Python, it will not overwrite other installs of other major versions. So installing Python 2.5.x will not overwrite Python 2.6.x, although installing 2.6.6 will overwrite 2.6.5.
So you can just install it. Then you call the Python version you want. For example:
C:\Python2.5\Python.exe
for Python 2.5 on windows and
C:\Python2.6\Python.exe
for Python 2.6 on windows, or
/usr/local/bin/python-2.5
or
/usr/local/bin/python-2.6
on Windows Unix (including Linux and OS X).
When you install on Unix (including Linux and OS X) you will get a generic python command installed, which will be the last one you installed. This is mostly not a problem as most scripts will explicitly call /usr/local/bin/python2.5 or something just to protect against that. But if you don't want to do that, and you probably don't you can install it like this:
./configure
make
sudo make altinstall
Note the "altinstall" that means it will install it, but it will not replace the python command.
On Windows you don't get a global python command as far as I know so that's not an issue.
Here's a quick hack:
Go to the directory of the version of python you want to run
Right click on python.exe
Select 'Create Shortcut'
Give that shortcut a name to call by( I use p27, p33 etc.)
Move that shortcut to your home directory(C:\Users\Your name)
Open a command prompt and enter name_of_your_shortcut.lnk(I use p27.lnk)
cp c:\python27\bin\python.exe as python2.7.exe
cp c:\python34\bin\python.exe as python3.4.exe
they are all in the system path, choose the version you want to run
C:\Users\username>python2.7
Python 2.7.8 (default, Jun 30 2014, 16:03:49) [MSC v.1500 32 bit (Intel)] on win
32
Type "help", "copyright", "credits" or "license" for more information.
>>>
C:\Users\username>python3.4
Python 3.4.1 (v3.4.1:c0e311e010fc, May 18 2014, 10:38:22) [MSC v.1600 32 bit Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>
The easiest way to run multiple versions of python on windows is described below as follows:-
1)Download the latest versions of python from python.org/downloads by selecting the relevant version for your system.
2)Run the installer and select Add python 3.x to the path to set path automatically in python 3 (you just have to click the checkbox). For python 2 open up your python 2 installer, select whatever preferences you want but just remember to set Add python.exe to path to Will be installed on local hard drive, Now just click next and wait for the installer to finish.
3)When both the installations are complete. Right click on my computer--Go to properties--Select advanced system settings--Go to environment variables--Click on new under System variables and add a new system variable with variable name as PY_PYTHON and set this variable value to 3. Now click on OK and you should be done.
4)Now to test this open the command prompt. Once you are in there type python or py, It should open up python3.
5)Now exit out of python3 by typing exit(). Now type py -2 it should open python 2.
If none of this works then restart the computer and if the problem still persists then uninstall everything and repeat the steps.
Thanks.
This is a simple and elegant solution to easily run 2 or more different versions of python without using scripts in Windows. Whatever the version of python, it will start from the Command prompt.
I have python versions 3.6.6 and 3.9. The Environment Variable paths are normal and were automatically added when each version of python was installed.
It's best to install python using the "all users" option. This way the python will simply install to:
C:\program files\python36
C:\program files\python39
Open each of these python folders and find the python.exe file. Copy and paste the python.exe file into those same folders. Then carefully rename the copies to:
python36.exe
python39.exe
Open and edit Environment Variables. Add 4 new User Variables.
C:\Program Files\Python36\Scripts
C:\Program Files\Python36\python36.exe
C:\Program Files\Python39\Scripts
C:\Program Files\Program39\python39.exe
Save and exit Environment Variables.
Open a new Command Prompt terminal window. To run one or the other version of python, type:
python36
python39
More versions of python can easily be added by repeating the same as shown above. Elegant and simple. Done.
Using a batch file to switch, easy and efficient on windows 7. I use this:
In the environment variable dialog (C:\Windows\System32\SystemPropertiesAdvanced.exe),
In the section user variables
added %pathpython% to the path environment variable
removed any references to python pathes
In the section system variables
removed any references to python pathes
I created batch files for every python installation (exmple for 3.4 x64
Name = SetPathPython34x64 !!! ToExecuteAsAdmin.bat ;-) just to remember.
Content of the file =
Set PathPython=C:\Python36AMD64\Scripts\;C:\Python36AMD64\;C:\Tcl\bin
setx PathPython %PathPython%
To switch between versions, I execute the batch file in admin mode.
!!!!! The changes are effective for the SUBSEQUENT command prompt windows OPENED. !!!
So I have exact control on it.
let's say if we have python 3.7 and python 3.6 installed.
they are respectively stored in following folder by default.
C:\Users\name\AppData\Local\Programs\Python\Python36
C:\Users\name\AppData\Local\Programs\Python\Python37
if we want to use cmd prompt to install/run command in any of the above specific environment do this:
There should be python.exe in each of the above folder.
so when we try running any file for ex. (see image1) python hello.py. we call that respective python.exe. by default it picks lower version of file. (means in this case it will use from python 3.6 )
image
so if we want to run using python3.7. just change the .exe file name. for ex. if I change to python37.exe and i want to use python3.7 to run hello.py
I will use python37 hello.py . or if i want to use python3.7 by default i will change the python.exe filename in python3.6 folder to something else . so that it will use python3.7 each time when I use only python hello.py
Shows your installed pythons
py -0
Uses version of python to do something
py -*version*
ex.
py -3.8 venv venv
Will create virtual environment in python 3.8
Note:
python -0
or
python -3.8
doesn't work, I assume it has to be "py"
You can create different python development environments graphically from Anaconda Navigator.
I had same problem while working with different python versions so I used anaconda navigator to create different python development environments and used different python versions in each environments.
Here is the help documentation for this.
https://docs.anaconda.com/anaconda/navigator/tutorials/manage-environments/
Introduce more details based on the answer given by #Aman.
Define different environment variables for different python versions.
For example:
You have E:\python2\python.exe and E:\python3\python.exe at the same time.
Then you can set an environment variable %python2% for E:\python2\python.exe and %python2% for E:\python3\python.exe.
Finally, when you want to run python2 (or python3), you can enter %python2% (or %python3%) directly in command prompt.
Here is a solution:
First, install all versions which you want to run in your pc. https://www.python.org/
Second, create virtual environment with which python version you want to use.
"py [python_version] -m venv [vritual_environment_name]" example: "py -3.9 -m venv env"
Note: You don't need to run "pip install virtualenv"
Using the Rapid Environment Editor you can push to the top the directory of the desired Python installation. For example, to start python from the c:\Python27 directory, ensure that c:\Python27 directory is before or on top of the c:\Python36 directory in the Path environment variable. From my experience, the first python executable found in the Path environment is being executed. For example, I have MSYS2 installed with Python27 and since I've added C:\MSYS2 to the path before C:\Python36, the python.exe from the C:\MSYS2.... folder is being executed.
I thought this answer might be helpful to others having multiple versions of python and wants to use pipenv to create virtual environment.
navigate to the project directory, and run py -[python version] pip install pipenv, example: py -3.6 pip install pipenv
run pipenv --python [version] to create the virtual environment in the version of the python you desire. example: pipenv --python 3.6
run pipenv shell to activate your virtual environment.
Just call the correct executable