如何在OS X上将Python的默认版本设置为3.x？

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?

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.

You can solve it by symbolic link.

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

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

Go to terminal type:

alias python=python3.x

This will setup default python as python3.x

The following worked for me

cd /usr/local/bin
mv python python.old
ln -s python3 python

I’m a little late to the game on this one, but I thought I should post an updated answer since I just encountered this issue for myself. 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

Once set, you can do:

which python

and it should show:

/usr/local/bin/python

You will have to reload your current terminal shell for it to use the new symlink in that shell, however, all newly opened shell sessions will (should) automatically use it. To test this, open a new terminal shell and run the following:

python --version

Go to ‘Applications’, enter ‘Python’ folder, there should be a bash script called ‘Update Shell Profile.command’ or similar. Run that script and it should do it.

Update: It looks like you should not update it: how to change default python version?

This worked for me. I added alias and restarted my terminal:

alias python=/usr/local/bin/python3

I believe most of people landed here are using ZSH thorugh iterm or whatever, and that brings you to this answer.

You have to add/modify your commands in ~/.zshrc instead.

I’m not sure if this is available on OS X, but on linux I would make use of the module command. See here.

Set up the modulefile correctly, then add something like this to your rc file (e.g. ~/.bashrc):

module load python3.3

This will make it so that your paths get switched around as required when you log in without impacting any system defaults.

I think when you install python it puts export path statements into your ~/.bash_profile file. So if you do not intend to use Python 2 anymore you can just remove that statement from there. Alias as stated above is also a great way to do it.

Here is how to remove the reference from ~/.bash_profile – vim ./.bash_profile – remove the reference (AKA something like: export PATH=”/Users/bla/anaconda:$PATH”) – save and exit – source ./.bash_profile to save the changes

$ sudo ln -s -f $(which python3) $(which python)

done.

The RIGHT and WRONG way to set Python 3 as default on a Mac

In this article author discuss three ways of setting default python:

1. What NOT to do.
2. What we COULD do (but also shouldn’t).
3. What we SHOULD do!

All these ways are working. You decide which is better.

If you are using a virtualenvwrapper, you can just locate it using which virtualenvwrapper.sh, then open it using vim or any other editor then change the following

# Locate the global Python where virtualenvwrapper is installed.
if [ "${VIRTUALENVWRAPPER_PYTHON:-}" = "" ]
then
    VIRTUALENVWRAPPER_PYTHON="$(command \which python)"
fi

Change the line VIRTUALENVWRAPPER_PYTHON="$(command \which python)" to VIRTUALENVWRAPPER_PYTHON="$(command \which python3)".

For me the solution was using PyCharm and setting the default python version to the the one that i need to work with.

install PyCharm and go to file ==> preferences for new project, then choose the interpreter you want for your projects, in this case python 3.3

If you use macports, you do not need to play with aliases or environment variables, just use the the method macports already offers, explained by this Q&A:

How to: Macports select python

TL;DR:

sudo port select --set python python27

If you are using macports, that has a easier way to do:

run:

port install python37

after install, set default:

sudo port select --set python python37

sudo port select --set python3 python37

restart your cmd window, finished.

Well… It’s kinda old. But still deserves a good answer.

And the good one is You Don’t Wanna Touch The Default Python On Mac.

Install any Python version you need via Homebrew or whatever and use it in virtualenv. Virtualenv is often considered to be something crap-like, but it’s still way, wayyyy better than changing python version system-wide (macOS is likely to protect itself from such actions) or user-wide, bash-wide… whatever. Just forget about the default Python. Using playgrounds like venv is what your OS will be most, very most grateful for.

The case is, for example, many modern Linux distributions get rid of Python2 installed out-of-the-box, leaving only Python3 in the system. But everytime you try to install something old with python2 as a dependency… hope you understand what I mean. A good developer doesn’t care. Good developers create clean playgrounds with python version they desire.

Mac users just need to run the following code on terminal

brew switch python 3.x.x

3.x.x should be the new python version.

This will update all the system links.

Suggestions to alias python to python3 will cause problems with virtual environments that set the version of python (eg: pyenv). With pyenv, you can set the version globally like so:

pyenv global 3.8.2

and then in any specific project, you can create a .python-version file which has the python version inside of it:

pyenv local 2.7.1

This is the best way to manage multiple versions of python on a system in my opinion.