How to set Python's default version to 3.x on OS X?

Question

I'm running Mountain Lion and the basic default Python version is 2.7. I downloaded Python 3.3 and want to set it as default.

Currently:

$ python
    version 2.7.5
$ python3.3
    version 3.3

How do I set it so that every time I run $ python it opens 3.3?

Solution 1

Changing the default python executable's version system-wide could break some applications that depend on python2.

However, you can alias the commands in most shells, Since the default shells in macOS (bash in 10.14 and below; zsh in 10.15) share a similar syntax. You could put alias python='python3' in your ~/.profile, and then source ~/.profile in your ~/.bash_profile and/or your~/.zsh_profile with a line like:

[ -e ~/.profile ] && . ~/.profile

This way, your alias will work across shells.

With this, python command now invokes python3. If you want to invoke the "original" python (that refers to python2) on occasion, you can use command python, which will leaving the alias untouched, and works in all shells.

If you launch interpreters more often (I do), you can always create more aliases to add as well, i.e.:

alias 2='python2'
alias 3='python3'

---

Tip: For scripts, instead of using a shebang like:

#!/usr/bin/env python

use:

#!/usr/bin/env python3

This way, the system will use python3 for running python executables.

Solution 2

You can solve it by symbolic link.

unlink /usr/local/bin/python
ln -s /usr/local/bin/python3.3 /usr/local/bin/python

Solution 3

Open ~/.bash_profile file.

vi ~/.bash_profile

Then put the alias as follows:

alias python='python3'

Now save the file and then run the ~/.bash_profile file.

source ~/.bash_profile

Congratulation !!! Now, you can use python3 by typing python.

python --version

Python 3.7.3

Solution 4

I encountered this issue as well, so I thought I should post an updated answer. Please note that this will only apply to a Mac-based setup (I haven't tried it with Windows or any flavor of Linux). The simplest way to get this working is to install Python via Brew. If you don't have brew installed, you will need to do that first. Once installed, do the following in at the terminal:

brew install python

This will install Python 3. After it's installed, run this:

ls -l /usr/local/bin/python*

You will see all of the links created by brew to its Python install. It will look something like this:

lrwxr-xr-x  1 username  admin  36 Oct  1 13:35 /usr/local/bin/python3@ -> ../Cellar/python/3.7.4_1/bin/python3
lrwxr-xr-x  1 username  admin  43 Oct  1 13:35 /usr/local/bin/python3-config@ -> ../Cellar/python/3.7.4_1/bin/python3-config
lrwxr-xr-x  1 username  admin  38 Oct  1 13:35 /usr/local/bin/python3.7@ -> ../Cellar/python/3.7.4_1/bin/python3.7
lrwxr-xr-x  1 username  admin  45 Oct  1 13:35 /usr/local/bin/python3.7-config@ -> ../Cellar/python/3.7.4_1/bin/python3.7-config
lrwxr-xr-x  1 username  admin  39 Oct  1 13:35 /usr/local/bin/python3.7m@ -> ../Cellar/python/3.7.4_1/bin/python3.7m
lrwxr-xr-x  1 username  admin  46 Oct  1 13:35 /usr/local/bin/python3.7m-config@ -> ../Cellar/python/3.7.4_1/bin/python3.7m-config

The first row in this example shows the python3 symlink. To set it as the default python symlink run the following:

ln -s -f /usr/local/bin/python3 /usr/local/bin/python

You will have to reload your current terminal shell to use the new symlink in that shell. Run this command to reload your shell:

exec $SHELL -l

You're all set now. Now, you can do:

which python

and it should show:

/usr/local/bin/python

All newly opened shell sessions will (should) automatically use the new symlink. To test this, open a new terminal shell and run the following:

python --version

Solution 5

Go to terminal type:

alias python=python3.x

This will setup default python as python3.x

View more solutions

Comments

[UnsettlingTrend]

Should this not be put in ~/.bash_profile instead of ~/.bash_aliases?

[Haymaker87]

Putting alias python=python3 and then running python in my terminal on osx el capitan didn't work for me. Tried saving it both ~/.bash_aliases and ~/.bash_profile.

[Wei Lu]

@Haymaker87 run source ~/.bash_profile after edit ~/.bash_profile file.

[tread]

You can do the same for pip: alias pip='pip3.6'

[Santosh Kumar]

@surfer190 that will cause problem when running with sudo, isn't it?

[Edison]

@SantoshKumar If you're using virtualenv/virtualenvwrapper for activation do you still need to use #!/usr/bin/env python3 or any other shebang + path at the top of python files?

[Alper]

Is this everything that is required for me to switch to python3 in my shell and applications?

[Santosh Kumar]

@Alper this was for shell only. The tip part is for developers, but don't change if either one of them is already there. It might break.

[Chad Befus]

This is the correct answer (aliases are nice but only accessible by bash, which limits where you can call from). However, I would use unlink instead of rm to remove symlinks (if you accidentally add a trailing slash on rm you might have some bad results). Alternatively, you could do ln -s -f ... which should overwrite the current symlink.

[Shin Kim]

@ChadBefus Thank you for your reply. I agree with your opinion. unlink is safer than rm.

[Anton Tarasenko]

Does it have any consequences for scripts that expect python to be python2.7?

[0x12]

It does not happen

[Jazzmine]

Can you do the reverse to reestablish python2x as the default version? So if you have linked python with python3, I'm suggesting then you can unlink python3 and ln -s python2.

[user924]

it does nothing

[MarksCode]

macOS: unlink: /usr/bin/python: Operation not permitted

[Henry Tseng]

Shouldn't cause any issues with sudo but will cause issues if you don't source your alias. This is more of a workaround.

[EliadL]

@MarksCode try to just run the second original line (i.e. ln -s... with /local/).

[Taylor A. Leach]

It won't take until you close your terminal window after the change to the .bash_profile are made.

[kidkkr]

If your app requires python3 for running, you should edit symlinks not alias.

[AlexeyGy]

you should set the pip alias not to pip3.6 specifically, instead set it to pip3: ``alias pip='pip3'

[Ani]

adding -> alias python='python3' in ~/.bash_profile file worked for me.

[jjwdesign]

For Mac OS users, you should use the brew commands to make the symlinks automatically. For example: brew unlink python, brew switch python 3.x.x_x (or 2.x.x), brew python link python (or python@2). Note, brew installs python 3 as "python3".

[Ganesh M S]

This did not work for me. After following this still python2 is invoked by default.

[Dani]

Would it still break things now in Catalina?

[Santosh Kumar]

Nope, its bash thing. Nothing to do with the operating system.

[Santosh Kumar]

Doesn't this risks the application dependent on python2? Definitely it will go away when Python 3 is mainstream, but still. Correct me if I'm missing something.

[Vlad K.]

The real major problem with recent Mac OSs is it doesn't give a $#%^ about UNIX commands and notion of root: >> sudo unlink /usr/bin/python Password: unlink: /usr/bin/python: Operation not permitted >> sudo -su root >> whoami root >> unlink /usr/bin/python unlink: /usr/bin/python: Operation not permitted

[SnellyBigoda]

If you found like I did that the same issue applies for pip (i.e. the pip --version is still 2.7.x) then you'll need to do the same steps for pip3. vi ~/.bash_profile, alias pip='pip3', source ~/.bash_profile, pip --version

[Discant]

This worked for me but using "alias python=python3"

[Ashwin R]

This will temporarily set python version for that terminal instance.

[Ricky Aguilar]

Do I need to source ~/.bash_profile everytime i close and open my terminal? It says command not found after I re-opened my terminal

[Ricky Aguilar]

Do I really need to source ~/.bash_profile everytime I re-opened my terminal? It reverts to python2 once I close and open the terminal again.

[Nepo Znat]

Works great (Reference)

[TimewiseGamgee]

This feels like the cleaner approach. I set mine to python 3.5 and it worked.

[Craig Conover]

Not sure why you got a down vote. This worked for me! Thanks for posing this. I upvoted you to cancel that down vote ;)

[Pei]

I had to close terminal and open a new one to get it working in macOS

[Robin]

Whilst this is a quick fix there are some potential issues with this solution, especially because you still depend on the python version Apple ships by default. This article explains them in depth as well as alternative solutions that avoid these problems.

[cs_pupil]

On Catalina (10.15.17), I get: Error: Calling `brew switch` is disabled! Use `brew link` @-versioned formulae instead.

[cs_pupil]

"You will have to reload your current terminal shell for it to use the new symlink in that shell." Thanks, that was the piece I was missing from all the answers so far.

[MIike Eps]

this does not work for me

[Nikhil Das Nomula]

I had to do this in my case ln -s -f /usr/local/Cellar/[email protected]/3.8.11/bin /usr/local/bin/python3

[iDevSpread]

It worked for me,tkx

[Xitcod13]

Error: Unknown command: switch

[sohammondal]

this also worked for me. A few things I would like to add - 1. I am using Mac M1, so I had to run arch -arm64 brew install python & 2. pip wasn't working for me, so I had to run sudo ln -s -f /usr/local/bin/pip3 /usr/local/bin/pip and then pip worked.

[sknight]

@sohammondal Thanks you. I appreciate your input.

[Mustafa]

ln: /usr/bin/python: Operation not permitted

[CN_Cabbage]

@RickyAguilar Me either. My current conda base is 3.8, I want to change the default pythton to 3.10. I have changed the ~/.bash_profile, by commenting out the existing one and adding export PATH="/Applications/anaconda3/envs/py3.10/bin:$PATH" it works after source. However, once I quite the terminal and reopen, it turns out the base is still py3.8. and i need to source again. Which is unresonable. Since I can conda activate py3.10. Have u find another way to tackle this?

[L. Heinrichs]

For me it looked like this: brew link [email protected]. Thanks for hints!

[Rohan Kumara]

if you already installed visual studio code it will be easy to use. code ~/.bash_profile instead of using. vi ~/.bash_profile.

[Rai Rz]

Just this code worked for my Mac, thanks