So I just installed the latest version of python, and I also changed the old 3.5 python version to 3.10 in my environment variables. There is no python 3.5 in the PATH inside environment variables, but when I run py --version in my CMD then it says version 3.5, but when I type python --version then it says version 3.10.2, is there a way to manually choose which version should be called on py or python?
You would need a python virtual environment to control it. (venv)
Just one thing, you can create a venv only with the version or python which is installed.
Also you can use conda to manage different version of python.
Here is a tutorial to create a venv or use conda on windows :
https://medium.com/co-learning-lounge/create-virtual-environment-python-windows-2021-d947c3a3ca78#a904
#The Mungax I am not sure but I can show you something that might help you
what is the Difference between “python” vs “py”
PYTHON
The command python refers to the Python executable of the default
Python installation. Technically, the path of this version is stored
inside the PATH environment variable where your OS will search for the
executable when processing any command.
PY
The command py refers to the Python launcher, a utility that’s
automatically installed into C:\Windows\ for any Python installation
on Windows. All files in the Windows folder are accessible without
needing to modify the PATH environment variable. Thus, the Python
launcher automatically delegates the work to the latest Python version
installed in your environment. However, you can also specify the used
installation by means of a flag argument such as in py -3.6 to specify
Python version 3.6.
I am trying to use Python3 with PyCharm.
So I installed Python(3.10.1) and PyCharm(2021.3.1)
But when I try to create a new project, PyCharm want me to choose 'base interpreter'
and I don't know which one to choose.
Here is the list of base interpreter:
I want to know what is difference between /usr/bin/python3 and Library/Frameworks/Python.framework/Versions/3.10/bin/python3
Usually the files under /usr/bin/ are symlinks to actual files, which means they are not real files but links to the actual file.
To see it for yourself go to the /usr/bin/ directory with a terminal and execute:
ls -a
I suppose macOS already ships with python and by installing Python 3.10 you added that last element to the list, which is also linked by /bin/usr/python3.
I'd go with /usr/bin/python3, more portable.
You can choose the one interpreter for the version of python you want. In your terminal, you can run python --version or python3 --version and it will display the version of python, Like this:
$ python --version
Python 2.7.16
$ python3 --version
Python 3.9.1
Performing which python, will give you the path to that python binary, like the following (although, this is where we are leaving "Python" and talking more about the OS and PATH.
$ which python3
/usr/local/bin/python3
For the other versions of Python you have installed, you can check their version by doing something like:
/Library/Frameworks/Python.framework/Versions/3.10/bin/python3 --version
You'll find that you may choose different versions of python for different projects. In the future, you may consider using venv to setup virtual python environments per project.
If you're just getting started with Python, I'd suggest sticking with the version you installed 3.10.1, and choosing that interpreter.
The base interpreter is the python.exe file that will run everything you do inside that project.
I would suggest you use Anaconda as a package manager and then create a virtual environment with the version of Python you need. Just follow these steps:
Getting started with Anaconda: https://docs.anaconda.com/anaconda/user-guide/tasks/pycharm/
Choosing an Anaconda virtual environment with Pycharm:
https://docs.anaconda.com/anaconda/user-guide/tasks/pycharm/
A package manager like Anaconda is very useful when working with Python.
Otherwise:
In your list you have many different versions of python. You should choose the base interpreter based on the python version you want to use.
Always select the latest version.
Since I use Python 3.9, it will be:
/usr/local/bin/python3.9
Based on your image, it would be:
/usr/local/bin/python3
The interpreter is what version your PyCharm project uses. It appears you have python2 and python3, so if you were writing in python2, you would use the python2 interpreter.
I would select the latest version, which in your case would be:
/usr/local/bin/python3
I have installed Anaconda3 just now, and I noticed that now, when I run python command from terminal, Python 3.5.1 |Anaconda 4.0.0 (64-bit)| is starting. Anaconda installer had added path to anaconda dir in $PATH and there is symlink from python to python3.5
My question is: will programs, that depends from python command and expects python2, work correctly, or I should remove symlink python from anaconda dir?
My question is: will programs, that depends from python command and
expects python2, work correctly?
Those programs should use full path of the python binary. Something like /usr/bin/python, and so $PATH is irrelevant. As long as you don't change /usr/bin/python, nothing will break.
If you remove the stuff that Anaconda has added, it's likely that Anaconda will not work properly.
That depends on your OS. Debian and Ubuntu both have ongoing projects to move the "default" version from 2 to 3 (also here). But it's not recommended to point /usr/bin/python to python3 if Python 2 is installed (see PEP 394).
If you want 'python' to be pointing to your 3.x install, you could use an alias (see here). This way you can use python in your session and at least don't change it on the whole system.
I have a big third-party python2.7 application, a bunch of python scripts, which is added into PATH and it requires python2.7 instead of python 3.5 which I have by default.
$ python
Python 3.5.1 (default, Mar 3 2016, 09:29:07)
[GCC 5.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>
$ python2
Python 2.7.11 (default, Mar 3 2016, 11:00:04)
[GCC 5.3.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
I run that application as $ some_app arg1 arg2. How can make it use python2 as a temporary solution, preferably only in that single terminal window?
I don't substitute a call of that application with "python". I call it like $ some_app arg1 arg2. I don't want to change the version of python permanently or modify the source code of the application.
My favorite way: use virtualenv or pyenv
The most used tool for keeping multiple Python environments is virtualenv. I like to use a sugary wrapper around it called virtualenvwrapper.
Usually I install it using:
sudo pip install virtualenvwrapper
Then I add a line like the following one to my shell profile:
source /usr/local/bin/virtualenvwrapper.sh
Now you can make a virtual environment for each version of Python. Gosh, you can make one for each Python project!
mkvirtualenv py3
mkvirtualenv py2 --python=python2
Then you can switch temporarily to python2 by typing:
workon py2
There is another tool called pyenv that lets you easily switch between multiple versions of Python. Quoting the project readme, "It's simple, unobtrusive, and follows the UNIX tradition of single-purpose tools that do one thing well. This project was forked from rbenv and ruby-build, and modified for Python". Looks like it is getting popular.
Both are elegant, easy to use and a perfect fit for this use case (switch to a particular python version in a terminal window temporarily).
The Unix way: set $PATH
It is a best practice to write the shebang for Python scripts like:
#!/usr/bin/env python
If the 3rd-party app you are running follows this convention, you can change the PATH. For example, suppose the default python interpreter is not the one you want:
$ env python --version
Python 3.5.1
Make a local copy of the python you want to make the default temporarily (you just have to do this one time):
$ mkdir ~/local
$ mkdir ~/local/python2
$ ln -s `which python2` ~/local/python2/python
Then every time you want to make python2 the default, do:
$ export PATH=~/local/python2/:$PATH
Now the default is the version you want:
$ env python --version
Python 2.7.10
The positive karma way: if the 3rd-party app has a hardcoded path in the shebang
Perhaps the app author did not follow the best practices and hardcoded the Python path in the shebang. For example, suppose the first line of the program is:
#!/usr/bin/python
In this case, none of the previous tricks would work. Personally, I would change it to the canonical form and send a pull request to the author of the 3rd-party app.
The bossy way: change the default Python version system-wide
While this does not really answer your question - because it affects every window and avery other user in the system - I'm mentioning it for the sake of completeness.
For example, if you are using Ubuntu you can change the default python interpreter using:
$ update-alternatives --config python
Other Linux distributions probably have something like this.
Quick and dirty
The shebang just tells the shell to call the script using the given interpreter. You can override the shebang when calling the app as interpreter app:
$ python2 `which app_name`
Or:
$ python2 /path/to/app_name
You can also just edit the program and change the shebang:
#!/usr/bin/python2
Note that this would change permanently the Python interpreter for that program, it is not temporary nor restricted to a particular terminal. Worst, if the program is in the global PATH, all the other users of the system will be affected. If you want to restore the old behavior, you must undo your changes.
That said, sometimes you just don't care about doing it right, you just want to make it work.
You can make use of terminal alias. The alias will not be temporary but it will not affect your system, so you can have a short alias like:
alias pyt "/usr/bin/python2.7"
in your .bashrc file inside home directory
As the question is tagged with Linux, I assume your scripts starts with that line
#! /usr/bin/env python
This is great to allow the system to choose the current Python installation, but here your requirement is to specifically use version 2.7
So IMHO you just have to change the hashbang line to select the required version:
#! /path/to/python-2.7
If you are using Anaconda as your Python distribution, it has virtual enviroments built in. If not, use virtualenv and virtualenvwrapper as Paul recommended.
In addition I recommend autoenv. With that you can automatically change your venv depending on the folder you're in. There is one for bash and one for zsh.
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