Change the Python3 default version in Ubuntu

Question

I am using Ubuntu 16.04 LTS . I have python3 installed. There are two versions installed, python 3.4.3 and python 3.6 . Whenever I use python3 command, it takes python 3.4.3 by default. I want to use python 3.6 with python3.

python3 --version shows version 3.4.3

I am installing ansible which supports version > 3.5 . So, whenever, I type ansible in the terminal, it throws error because of python 3.4

sudo update-alternatives --config python3
update-alternatives: error: no alternatives for python3

What does your sudo update-alternatives --config python3 say? — Mikael Kjær, Dec 13 '17 at 09:35
See my comment in the below answer on how to use ansible with a specific version of python3. You could also consider removing python 3.4. — Mikael Kjær, Dec 13 '17 at 09:43
@Mikael Different Python versions are not alternatives on Ubuntu. The OS relies on a specific version (or versions) being installed. — wjandrea, Jan 01 '20 at 19:22
Best / safest to add alias python3="python3.6" to ~/.bash_profile — goonerify, Oct 08 '21 at 11:19

GAD3R · Answer 1 · 2018-11-26T10:01:12.917

427

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

edited Nov 26 '18 at 10:01

answered Dec 14 '17 at 12:11

GAD3R

66,769

35

This answer will probably break apt. After selecting a different version of python try to run sudo apt update. If it gives you an error like ModuleNotFoundError: No module named 'apt_pkg' you want to go to /usr/lib/python3/dist-packages and create the symlink: ln -s apt_pkg.cpython-{34m,36m}-x86_64-linux-gnu.so. – Giacomo Alzetta May 30 '19 at 08:22
It gives me an error: $ sudo update-alternatives --set python /usr/bin/python3.6 update-alternatives: error: no alternatives for python Any suggestions? – Slava Fomin II Sep 10 '19 at 15:34
1

@GAD3R Thanks. I've managed to create a symlink manually to point to the Python 3.6. Also, I don't have 3.7 installed. – Slava Fomin II Sep 11 '19 at 08:58
15

Making python3 point to python3.8 with this method broke gnome-terminal for me. – Oct 17 '19 at 23:49
1

@Boris Did you find a way to point to python3.8 succesfully? – Johny Nov 25 '19 at 20:06
13

@Johny I just added alias python="python3.8" to ~/.bash_profile – Nov 25 '19 at 21:02
1

@Boris Yes, I ended up doing the same. – Johny Nov 27 '19 at 01:47
11

Don't do this. It will break apt like @Giacomo mentioned along with other OS components like do-release-upgrade. Simply use an alias instead. – wjandrea Jan 01 '20 at 19:15
@Boris I personally do not like to clutter my .bash_profile with aliases. And by the way, what happens when you use another shell? ;) – loved.by.Jesus Jan 07 '20 at 14:23
I had an error update-alternatives: error: alternative link /usr/bin/python is already managed by python. So I could not use the update-alternatives method. The only solution is to change the symlink as in @IRSHAD answer below. – loved.by.Jesus Jan 07 '20 at 14:44
2

Works fine in Ubuntu 18.04 LTS without breaking APT.
Note to those confused: if you are getting the error: no alternatives for python message, then you need to run the --install commands following first (replacing the python versions you want to use as appropriate, and the numbers at the end are just for order) then you run the --config command again and you will be asked which version you want to use by default.
– tpartee Feb 25 '20 at 06:50
1

this helped to me sudo ln -s apt_pkg.cpython-36m-x86_64-linux-gnu.so apt_pkg.so to repair no module named apt-get. – Michael D Mar 25 '21 at 13:15
In Ubuntu 22, this gives: update-alternatives: error: no alternatives for python – Cerin Jul 04 '22 at 01:01
@Cerin Please ask a new detailed question. Which python version you have installed? – GAD3R Jul 13 '22 at 21:16

score 74 · Answer 2 · edited Nov 18 '22 at 10:28

74

You can achieve this by applying below simple steps -

Check python version on terminal: python --version

Execute this command to switch to python 3.6:

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

Check python version: python --version
Done.

edited Nov 18 '22 at 10:28

Kusalananda

333,661

answered Feb 02 '19 at 09:37

user12979326

873

Works fine on Ubuntu 18.04. so simple than other solutions. thanks a lot – Mohammad Heydari Aug 13 '19 at 23:29
@Sam-T your comment didn't work for me. I am on Debian 10 & this worked for me sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.7 1; python --version – Kumar Apr 14 '20 at 03:47
This command doesn't change the behavior for dependencies such as pip. After executing this, pip was still using the older version of python. – Amir Zare Oct 05 '23 at 10:46

score 43 · Answer 3 · answered May 25 '19 at 18:03

43

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 '19 at 18:03

IRSHAD

647

1

I agree this answer is the best. However, I would add that some people's newly installed python won't be located in /usr/bin/pythonX.X. Instead figure out the location with which pythonX.X and substitute in. – Gabe Morris Jan 19 '22 at 01:07
I couldn't find the newly installed python3.9 in /user/bin/, any suggestion please? I am on Ubuntu 18.04 – Adamy Jun 17 '22 at 00:37
Note that if you don't have root permission, then u may need execute the above commands with sudo. – Bowen Xu Jul 22 '22 at 04:41
I needed this variation: sudo unlink /usr/bin/python3, sudo ln -s /usr/bin/python3.8 /usr/bin/python3, python3 --version – small mammal Jun 25 '23 at 23:26

score 27 · Answer 4 · edited Mar 11 '20 at 13:51

27

Using these commands can help you:

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

edited Mar 11 '20 at 13:51

Verena Praher

103

answered Nov 08 '18 at 11:44

Newt

419

1

thanks but after restarting the computer the main python would be still the ex python 2.7 – Mohammad Heydari Aug 13 '19 at 23:25
3

You should add the script to modify the default in ~/.bashrc. Then you will make it work forever. – Newt Nov 04 '19 at 13:32
like this: export python=/home/xxx (your py3 directory) – Newt Nov 04 '19 at 13:40

score 14 · Answer 5 · edited Aug 24 '20 at 14:42

14

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

edited Aug 24 '20 at 14:42

Stewart

13,677

answered May 21 '19 at 10:29

mmblack

157

1

nit: you don't have folders under bin, you have executables. – mayid Oct 01 '20 at 22:52
Didn't work for me. – Evan Zamir Sep 06 '21 at 00:15
1

This broke sudo apt-get update for me ModuleNotFoundError: No module named 'apt_pkg' – Mark Dec 07 '21 at 22:51

score 6 · Answer 6 · edited Nov 25 '19 at 07:58

6

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

edited Nov 25 '19 at 07:58

Adersh Ps

3
3

answered Dec 04 '18 at 11:13

nabi sheyhov

93

4

This broke apt installer. – jws May 05 '20 at 21:30

score 5 · Answer 7 · 2017-12-13T09:46:17.280

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

Actually, I am installing ansible , which supports only > python 3.5 — codeclue, Dec 13 '17 at 09:35
You can set the ansible_python_interpreter variable to use your python3.6. http://docs.ansible.com/ansible/latest/python_3_support.html — Mikael Kjær, Dec 13 '17 at 09:37

score 4 · Answer 8 · answered Mar 13 '19 at 20:02

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.

This is one of only 2 answers that updates python3 without updating the python version and this one seems to have been first. Thanks!! — sage, Aug 12 '21 at 18:39

score 1 · Answer 9 · answered Jul 20 '23 at 00:09

1

As mentioned in this comment by Slion,sudo apt install python-is-python3 will do this for you in a reasonable way, currently IIUC by added an appropriate symlink.

answered Jul 20 '23 at 00:09

Karol

225
2
5

score 0 · Answer 10 · answered May 21 '19 at 10:42

0

You can change the simbolic link by ln -sf python3.6 python3 inside /usr/bin. With this when you call python3 it will execute python3.6

answered May 21 '19 at 10:42

SPAWN35

53
9

Change the Python3 default version in Ubuntu

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