As you can see, I have both Python2 and Python3 installed.
I hope you know that the path of the python executable has to be added to the PATH environment variable in Windows. As you can see, the path of Python2 is placed above the path of Python3 in my system.
How does the cmd run commands?
It searches for an executable with the same name in the directory the cmd has been opened in, then goes and searches for the command in the locations provided in the Windows PATH variable, from TOP to BOTTOM.
Which means, it gets the path to Python2 before it can get to the path of Python3. Therefore, every time you type python in your cmd, it runs Python2.
Both Python2 and Python3 executables have the same name in Windows so it never runs python3.
What seems like an obvious solution?
You might think, changing the name of python.exe to python3.exe for the Python3 executable will solve your problem. You are partially right, it will work. But you have to use python3 file.py or python3 --version, which I think, is understandable. But, pip will no longer work if you change the name of the original python executable. You will no longer be able to install external packages and modules.
How can this problem be solved?
You can create an alias for the Python3 executable called python3.bat.
.exe and .bat files can be called from the cmd directly without using their extension. We always write python filename.py instead of python.exe filename.py although both are correct. The same can be done with .bat files.
Go back to the first image and notice the python3.bat file below python.exe. That is my way of calling python3 without renaming my original python executable.
python3.bat
Create a new file using notepad or something and paste this %~dp0python %*
I don't fully understand how this works except that dp0 basically runs python from inside the same directory and %* passes all the arguments to the python executable. Place this file inside your Python3 installation directory and your problem will hopefully be solved.
python3 basically runs your python3.bat file, which in turn runs the python.exe from its folder and passes the arguments to it.
I hope this solves your problem.
Answer from Diptangsu Goswami on Stack Overflow
As you can see, I have both Python2 and Python3 installed.
I hope you know that the path of the python executable has to be added to the PATH environment variable in Windows. As you can see, the path of Python2 is placed above the path of Python3 in my system.
How does the cmd run commands?
It searches for an executable with the same name in the directory the cmd has been opened in, then goes and searches for the command in the locations provided in the Windows PATH variable, from TOP to BOTTOM.
Which means, it gets the path to Python2 before it can get to the path of Python3. Therefore, every time you type python in your cmd, it runs Python2.
Both Python2 and Python3 executables have the same name in Windows so it never runs python3.
What seems like an obvious solution?
You might think, changing the name of python.exe to python3.exe for the Python3 executable will solve your problem. You are partially right, it will work. But you have to use python3 file.py or python3 --version, which I think, is understandable. But, pip will no longer work if you change the name of the original python executable. You will no longer be able to install external packages and modules.
How can this problem be solved?
You can create an alias for the Python3 executable called python3.bat.
.exe and .bat files can be called from the cmd directly without using their extension. We always write python filename.py instead of python.exe filename.py although both are correct. The same can be done with .bat files.
Go back to the first image and notice the python3.bat file below python.exe. That is my way of calling python3 without renaming my original python executable.
python3.bat
Create a new file using notepad or something and paste this %~dp0python %*
I don't fully understand how this works except that dp0 basically runs python from inside the same directory and %* passes all the arguments to the python executable. Place this file inside your Python3 installation directory and your problem will hopefully be solved.
python3 basically runs your python3.bat file, which in turn runs the python.exe from its folder and passes the arguments to it.
I hope this solves your problem.
You should have python3 also in your path. You could use python3 to run your script:
python3 <your_script>
But to answer your question, you could use alias and update it as python.
$ python --version
Python 2.7.6
$ alias python=python3
$ python --version
Python 3.6.4
Generally i was using the latest python version 3.12. in my terminalk
So when i created a virtual environment with
python -m venv xyz
the created virtual environment was under 3.12
For testing purposes it was now necessary to also install python version 3.9.
But now when i am using venv to create a new virtual environment it is the version 3.9.
How can i change the "standard" python-version bakc to 3.12. when i am creating a virtual environment using venv?
How to change default python in `py-launcher` at windows?
Switching between versions of python installed from microsoft store
windows - How to run different python versions in cmd - Stack Overflow
Changing default version of python from 2,7.16 to 3.12.1
Videos
This is most likely due to the path variable. You can see this in a command window by typing
Path
at your prompt.
To update the settings,
- Open the 'System' properties.
- Open Environment Variables
- Highlight the 'Path' Variable and click edit.
- Edit the values for the Python entries, to point to the desired python version.
- OK on all boxes, close any CMD windows open, and open new one. Python command should now reference the correct location.
Solution refers to Windows 10, but is essentially the same on Windows 7 +
I was having the same issue as the older python executable was in my system space (which I have no access to) and the newer version is in the user space.
The work around I thought of was to create a .bat file which will open a CMD window in the user space python version.
new_python.bat:
@set "PATH=C:\Users\USER\AppData\Local\Programs\Python\Python39\;C:\Users\USER\AppData\Local\Programs\Python\Python39\Scripts\;%PATH%"
@cmd /k python --version
Does a decent job for me. Just change the first two lines in the PATH variable to your Python directory and the Python Scripts directory. The CMD which will open using this bat will be ready to run the newer version of python executable.
To change the python version for your terminal session you can create an alias in your .bashrc file then re-login.
alias python='/usr/bin/python3.4'
The link to the following article provides detailed instructions to change to an alternate Python version per user session.
My recommendation would be to use an alias to "override" the python command.
An alias can be created with the same name as the core name of a command (i.e., a command without any options or arguments). In such case, it is the alias that is called (i.e., activated) first when the name is used, rather than the command with the same name. For example, an alias named ls could be created for the command ls -al as follows:
alias ls="ls -al"ls is a commonly used command that by default lists the names of the files and directories within the current directory (i.e., the directory in which the user is currently working). The -a option instructs ls to also show any hidden files and directories, and the -l option tells it to provide detailed information about each file and subdirectory.
Such an alias can be disabled temporarily and the core command called by preceding it directly (i.e., with no spaces in between) with a backslash, i.e.,
\ls
Taken from linfo.org
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\Scriptsto environment variablePATH. - Go to
C:\Python35to renamepython.exetopython3.exe, also toC:\Python27, renamepython.exetopython2.exe. - restart your command window.
- type
python2 scriptname.py, orpython3 scriptname.pyin 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.
You can use explicit paths:
c:\python26\python setup.py install
c:\python25\python setup.py install
Recent versions of Python install PyLauncher. It is installed in the path so no need to add an explicit Python to the path, and it allows easy switching between multiple Python versions.
Examples:
py -3 setup.py # run latest Python 3
py -2 setup.py # run latest Python 2
py -3.3
py -2.7-32 # use 32-bit version
py # run default version
The default version can be specified in the environment variable PY_PYTHON, e.g. PY_PYTHON=3 (latest Python 3).
It depends on your operating system. If you have python 2.6 installed, you need to change your environment path to point to the 2.6 executable rather than the 2.5 executable. Do a Google search for changing your PATH variable on your operating system.
This is if you have both the versions installed.
Go to This PC → Right-click → Click on Properties → Advanced System Settings.
You will see the System Properties. From here navigate to the Advanced Tab -> Click on Environment Variables.
You will see a top half for the user variables and the bottom half for System variables.
Check the System Variables and double-click on the Path (to edit the Path).
Check for the path of Python(which you wish to run i.e. Python 2.x or 3.x) and move it to the top of the Path list.
Restart the Command Prompt, and now when you check the version of Python, it should correctly display the required version.
The Python installer installs Python Launcher for Windows. This program (py.exe) is associated with the Python file extensions and looks for a "shebang" comment to specify the python version to run. This allows many versions of Python to co-exist and allows Python scripts to explicitly specify which version to use, if desired. If it is not specified, the default is to use the latest Python version for the current architecture (x86 or x64). This default can be customized through a py.ini file or PY_PYTHON environment variable. See the docs for more details.
Newer versions of Python update the launcher. The latest version has a py -0 option to list the installed Pythons and indicate the current default. py -h lists complete Python Launcher options as well as Python options.
Here's how to check if the launcher is registered correctly from the console:
C:\>assoc .py
.py=Python.File
C:\>ftype Python.File
Python.File="C:\Windows\py.exe" "%1" %*
Above, .py files are associated with the Python.File type. The command line for Python.File is the Python Launcher, which is installed in the Windows directory since it is always in the PATH.
For the association to work, run scripts from the command line with script.py, not "python script.py", otherwise python will be run instead of py. If fact it's best to remove Python directories from the PATH, so "python" won't run anything and enforce using py.
py.exe can also be run with switches to force a Python version:
py -3 script.py # select latest Python 3.X version to be used.
py -3.6 script.py # select version 3.6 specifically.
py -3.9-32 script.py # select version 3.9 32-bit specifically.
py -0 # list installed Python versions (latest PyLauncher).
Additionally, add .py;.pyw;.pyc;.pyo to the PATHEXT environment variable and then the command line can just be script with no extension.
I have macOS and downloaded VSCode which I think comes with Python 3.12. Then, I downloaded Python 3.8 from the official website. Now, Python 3.8 is the default version. How can I switch default to Python 3.12 without deleting 3.8? Thanks in advance!