Как изменить версию python linux

asked Dec 13, 2017 at 9:13

From the comment:

sudo update-alternatives --config python

Will show you an error:

update-alternatives: error: no alternatives for python3 

You need to update your update-alternatives , then you will be able to set your default python version.

sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.4 1
sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.6 2

Then run :

sudo update-alternatives --config python

Set python3.6 as default.

Or use the following command to set python3.6 as default:

sudo update-alternatives  --set python /usr/bin/python3.6

answered Dec 14, 2017 at 12:11

You can achieve this by applying below simple steps —

1. Check python version on terminal: python --version

2. Execute this command to switch to python 3.6:

   sudo update-alternatives --install /usr/bin/python python /usr/bin/python3 1
   

3. Check python version: python --version

4. Done.

if you have multiple version of python in your system. You just need to update the symbolic link of python inside /usr/bin/

root@irshad:/usr/bin# ls -lrth python*
lrwxrwxrwx 1 root root    9 Apr 16  2018 python -> python2.7
-rwxr-xr-x 1 root root 3.6M Nov 12  2018 python2.7
-rwxr-xr-x 2 root root 4.4M May  7 14:58 python3.6

In above example if you see the output of python --version you will get python2.7

Now update the python symlink using below command-

root@irshad:/usr/bin# unlink python
root@irshad:/usr/bin# ln -s /usr/bin/python3.6 python
root@irshad:/usr/bin# python --version
Python 3.6.8

answered May 25, 2019 at 18:03

Using these commands can help you:

1. check the version of python:
   ls /usr/bin/python*
2. alias:
   alias python='/usr/bin/pythonxx' (add this to . ~/.bashrc)
3. re-login or source . ~/.bashrc
4. check the python version again:
   python --version

First check that you have a python3.6 folder?

ls /usr/bin/python3.6

If you have «python3.6» folder, you are good to go. Now update-alternatives

sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.6 1

then update new config for python3

sudo update-alternatives --config python3

Finally, check default python3 version:

python3 --version

Create symlink for /usr/bin/python3.
In my LinuxMint:

# ls -lh /usr/bin/python3 /usr/bin/python
lrwxrwxrwx 1 root root 9 ноя 24  2017 /usr/bin/python -> python2.7
lrwxrwxrwx 1 root root 9 сен  6  2017 /usr/bin/python3 -> python3.5

# mv /usr/bin/python /usr/bin/python.bak
# cp /usr/bin/python3 /usr/bin/python
# python --version
Python 3.5.2

An easy answer would be to add an alias for python3.6.

Just add this line in the file ~/.bashrc : alias python3="python3.6", then close your terminal and open a new one. Now when you type python3 xxx it gets translated to python3.6 xxx.

This solution fixes your problem without needing to tweak your system too heavily.

EDIT :

As Mikael Kjær pointed out, this is a misconfiguration of ansible with your system.

As seen here :

Set the ansible_python_interpreter configuration option to
/usr/bin/python3. The ansible_python_interpreter configuration option
is usually set per-host as an inventory variable associated with a
host or group of hosts:

  # Example inventory that makes an alias for localhost that uses python3
  [py3-hosts]
  localhost-py3 ansible_host=localhost ansible_connection=local

  [py3-hosts:vars]
  ansible_python_interpreter=/usr/bin/python3

As seen here about the config file :

Changes can be made and used in a configuration file which will be processed in the following order:

* ANSIBLE_CONFIG (an environment variable)
* ansible.cfg (in the current directory)
* .ansible.cfg (in the home directory)
* /etc/ansible/ansible.cfg

answered Dec 13, 2017 at 9:27

update-alternatives is to change system symlinks to user-defined/admin-defined symlinks.
If you have multiple versions of python3 installed in your system and want to control which python3 version to invoke when python3 is called. Do the following

sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.4 1
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.5 2

Run below command if you want to change priority in the future.

update-alternatives --config python3

Explanation:-

sudo update-alternatives --install <symlink_origin> <name_of_config> <symlink_destination> <priority>

You can go on change name_of_config to python4, but then you have to invoke update-alternatives —config with python4 to reconfigure.

Using this approach you are able to control system python version and python3 version separately.

answered Mar 13, 2019 at 20:02

asked Feb 1, 2017 at 17:57

The second line mentioned can be changed to

[sudo] update-alternatives --install /usr/bin/python python /usr/bin/python3 10

This gives a priority of 10 for the path of python3.

The disadvantage of alternatively editing .bashrc is that using the commands with sudo will not work.

EDIT:

I wrote this when I was young and naive, update-alternatives is the better way to do this. See @Pardhu’s answer.

Outdated answer:

Open your .bashrc file nano ~/.bashrc. Type alias python=python3
on to a new line at the top of the file then save the file with ctrl+o
and close the file with ctrl+x. Then, back at your command line type
source ~/.bashrc. Now your alias should be permanent.

To change Python 3.6.8 as the default in Ubuntu 18.04 to Python 3.7.

Install Python 3.7

Steps to install Python3.7 and configure it as the default interpreter.

1. Install the python3.7 package using apt-get

   sudo apt-get install python3.7

2. Add Python3.6 & Python 3.7 to update-alternatives

sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.6 1
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.7 2

1. Update Python 3 to point to Python 3.7

   sudo update-alternatives --config python3
   Enter 2 for Python 3.7

2. Test the version of python

python3 --version
Python 3.7.1 

If you have Ubuntu 20.04 LTS (Focal Fossa) you can install python-is-python3:

sudo apt install python-is-python3

which replaces the symlink in /usr/bin/python to point to /usr/bin/python3.

answered May 18, 2020 at 20:12

answered Feb 1, 2017 at 18:00

Update:
Since Ubuntu 20.04, the python3 is the default version, but still, python is not registered as python3 by default. In order to make that happen, you can simply do :

sudo apt install python-is-python3

For more information you can check this out.
Old way:

Do

cd ~
gedit .bash_aliases

then write either

alias python=python3

or

alias python='/usr/bin/python3'

Save the file, close the terminal and open it again.
You should be fine now! Link

answered Sep 15, 2017 at 18:34

A simple safe way would be to use an alias. Place this into ~/.bashrc file:
if you have gedit editor use

gedit ~/.bashrc

to go into the bashrc file and then at the top of the bashrc file make the following change.

alias python=python3

After adding the above in the file. run the below command

source ~/.bash_aliases or source ~/.bashrc

example:

$ python —version

Python 2.7.6

$ python3 —version

Python 3.4.3

$ alias python=python3

$ python —version

Python 3.4.3

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Simply remove python-is-python2:

sudo apt purge python-is-python2

And install python-is-python3:

sudo apt install python-is-python3

It will automate the process of transition to new python3. Optionally you can get rid of remaining packages later:

sudo apt autoremove && sudo apt autoclean

answered May 25, 2020 at 8:22

       ~$ sudo apt-get install python3.9
/usr/bin$ cd /usr/bin
/usr/bin$ sudo unlink python3
/usr/bin$ sudo ln -sv /usr/bin/python3.9 python3
/usr/bin$ python3 --version
          Python 3.9.5
/usr/bin$ pip3 --version
          pip 20.0.2 from /usr/lib/python3/dist-packages/pip (python 3.9)

answered Jan 3, 2022 at 3:46

Mian Asbat AhmadMian Asbat Ahmad

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sudo rm /usr/bin/python3 #remove existing link
sudo ln /usr/bin/python3.8 /usr/bin/python3 # create a new link to the version of your choice

answered Oct 1, 2021 at 9:11

JanPoJanPo

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At first, Make sure Python3 is installed on your computer

Go to your terminal and type:

cd ~/ to go to your home directory

If you didn’t set up your .bash_profile yet, type touch .bash_profile to create your .bash_profile.

Or, type open -e .bash_profile to edit the file.

Copy and save alias python=python3 in the .bash_profile.

Close and reopen your Terminal. Then type the following command to check if Python3 is your default version now:

python --version

You should see python 3.x.y is your default version.

Cheers!

answered Sep 21, 2019 at 19:13

You probably don’t actually want to change your default Python.

Your distro installed a standard system Python in /usr/bin, and may have scripts that depend on this being present, and selected by #! /usr/bin/env python. You can usually get away with running Python 2.6 scripts in 2.7, but do you want to risk it?

On top of that, monkeying with /usr/bin can break your package manager’s ability to manage packages. And changing the order of directories in your PATH will affect a lot of other things besides Python. (In fact, it’s more common to have /usr/local/bin ahead of /usr/bin, and it may be what you actually want—but if you have it the other way around, presumably there’s a good reason for that.)

But you don’t need to change your default Python to get the system to run 2.7 when you type python.

First, you can set up a shell alias:

alias python=/usr/local/bin/python2.7

Type that at a prompt, or put it in your ~/.bashrc if you want the change to be persistent, and now when you type python it runs your chosen 2.7, but when some program on your system tries to run a script with /usr/bin/env python it runs the standard 2.6.

Alternatively, just create a virtual environment out of your 2.7 (or separate venvs for different projects), and do your work inside the venv.

answered Oct 8, 2013 at 19:17

Add /usr/local/bin to your PATH environment variable, earlier in the list than /usr/bin.

Generally this is done in your shell’s rc file, e.g. for bash, you’d put this in .bashrc:

export PATH="/usr/local/bin:$PATH"

This will cause your shell to look first for a python in /usr/local/bin, before it goes with the one in /usr/bin.

(Of course, this means you also need to have /usr/local/bin/python point to python2.7 — if it doesn’t already, you’ll need to symlink it.)

answered Oct 8, 2013 at 19:08

Enter the command

which python

//output:
/usr/bin/python

cd /usr/bin
ls -l

Here you can see something like this

lrwxrwxrwx 1 root   root            9 Mar  7 17:04  python -> python2.7

your default python2.7 is soft linked to the text ‘python’

So remove the softlink python

sudo rm -r python

then retry the above command

ls -l

you can see the softlink is removed

-rwxr-xr-x 1 root   root      3670448 Nov 12 20:01  python2.7

Then create a new softlink for python3.6

ln -s /usr/bin/python3.6 python

Then try the command python in terminal

//output:
Python 3.6.7 (default, Oct 22 2018, 11:32:17) 
[GCC 8.2.0] on linux

Type help, copyright, credits or license for more information.

Shiv BuyyaShiv Buyya

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KishoreKishore

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I guess you have installed the 2.7 version manually, while 2.6 comes from a package?

The simple answer is: uninstall python package.

The more complex one is: do not install manually in /usr/local. Build a package with 2.7 version and then upgrade.

Package handling depends on what distribution you use.

answered Oct 8, 2013 at 19:08

You probably don’t actually want to change your default Python.

Your distro installed a standard system Python in /usr/bin, and may have scripts that depend on this being present, and selected by #! /usr/bin/env python. You can usually get away with running Python 2.6 scripts in 2.7, but do you want to risk it?

On top of that, monkeying with /usr/bin can break your package manager’s ability to manage packages. And changing the order of directories in your PATH will affect a lot of other things besides Python. (In fact, it’s more common to have /usr/local/bin ahead of /usr/bin, and it may be what you actually want—but if you have it the other way around, presumably there’s a good reason for that.)

But you don’t need to change your default Python to get the system to run 2.7 when you type python.

First, you can set up a shell alias:

alias python=/usr/local/bin/python2.7

Type that at a prompt, or put it in your ~/.bashrc if you want the change to be persistent, and now when you type python it runs your chosen 2.7, but when some program on your system tries to run a script with /usr/bin/env python it runs the standard 2.6.

Alternatively, just create a virtual environment out of your 2.7 (or separate venvs for different projects), and do your work inside the venv.

answered Oct 8, 2013 at 19:17

Add /usr/local/bin to your PATH environment variable, earlier in the list than /usr/bin.

Generally this is done in your shell’s rc file, e.g. for bash, you’d put this in .bashrc:

export PATH="/usr/local/bin:$PATH"

This will cause your shell to look first for a python in /usr/local/bin, before it goes with the one in /usr/bin.

(Of course, this means you also need to have /usr/local/bin/python point to python2.7 — if it doesn’t already, you’ll need to symlink it.)

answered Oct 8, 2013 at 19:08

Enter the command

which python

//output:
/usr/bin/python

cd /usr/bin
ls -l

Here you can see something like this

lrwxrwxrwx 1 root   root            9 Mar  7 17:04  python -> python2.7

your default python2.7 is soft linked to the text ‘python’

So remove the softlink python

sudo rm -r python

then retry the above command

ls -l

you can see the softlink is removed

-rwxr-xr-x 1 root   root      3670448 Nov 12 20:01  python2.7

Then create a new softlink for python3.6

ln -s /usr/bin/python3.6 python

Then try the command python in terminal

//output:
Python 3.6.7 (default, Oct 22 2018, 11:32:17) 
[GCC 8.2.0] on linux

Type help, copyright, credits or license for more information.

Shiv BuyyaShiv Buyya

3,53929 silver badges24 bronze badges

KishoreKishore

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I guess you have installed the 2.7 version manually, while 2.6 comes from a package?

The simple answer is: uninstall python package.

The more complex one is: do not install manually in /usr/local. Build a package with 2.7 version and then upgrade.

Package handling depends on what distribution you use.

answered Oct 8, 2013 at 19:08