How to Use Brew Installed Python as the Default Python

brew-installed Python not overriding system python

TL;DR Add the following to your .bash_profile (or equivalent):

export PATH="/usr/local/opt/python/libexec/bin:$PATH"

Explanation

It seems python via homebrew is now handled differently (see https://docs.brew.sh/Homebrew-and-Python).

python3 points to Homebrew’s Python 3.x (if installed)

python2 points to Homebrew’s Python 2.7.x (if installed)

python points to Homebrew’s Python 2.7.x (if installed) otherwise the macOS system Python. Check out brew info python if you wish to add
Homebrew’s 3.x python to your PATH.

Checking out brew info python hints at what you need to do:

Unversioned symlinks python, python-config, pip etc. pointing to
python3, python3-config, pip3 etc., respectively, have been
installed into /usr/local/opt/python/libexec/bin

The hint being that you therefore have to add /usr/local/opt/python/libexec/bin before /usr/bin in your path (not /usr/local/bin as stated in some sources e.g. https://docs.python-guide.org/starting/install3/osx/)

See also https://github.com/Homebrew/homebrew-core/issues/15746

Switching Python version installed by Homebrew

There is an Homebrew known issue related to side by side install of Python 3.8 / 3.9. To workaround, following commands should work for you:

brew unlink python@3.9
brew unlink python@3.8
brew link --force python@3.9

Re-opening your terminal or execute command rehash can be required to take account the change.

How to default Python3.8 on my Mac using Homebrew?

Here is the solution:

If existing symlinks belong to python 3.7 you should unlink them:

brew unlink python

Basically all you need to do:

brew link --force python@3.8

OR force the link and overwrite all conflicting files:

brew link --force --overwrite python@3.8

OR if needed list all files that would be deleted:

brew link --overwrite --dry-run python@3.8

Thus you can switch to any python version available in the Homebrew repo.

Also check out this answer for pyenv usage

Make python3 as my default python on Mac

Probably the safest and easy way is to use brew and then just modify your PATH:

First update brew:

brew update

Next install python:

brew install python

That will install and symlink python3 to python, for more details do:

brew info python

Look for the Caveats:

==> Caveats
Python has been installed as
  /usr/local/bin/python3

Unversioned symlinks `python`, `python-config`, `pip` etc. pointing to
`python3`, `python3-config`, `pip3` etc., respectively, have been installed into
  /usr/local/opt/python/libexec/bin

Then add to your path /usr/local/opt/python/libexec/bin:

export PATH=/usr/local/opt/python/libexec/bin:$PATH

The order of the PATH is important, by putting first the /usr/local/opt/python/libexec/bin will help to give preference to the brew install (python3) than the one is in your system located in /usr/bin/python

How to make Mac OS use the python installed by Homebrew

If you want to install Python 3 using Homebrew:

$ brew install python3
==> Downloading http://python.org/ftp/python/3.3.0/Python-3.3.0.tar.bz2
Already downloaded: /Library/Caches/Homebrew/python3-3.3.0.tar.bz2
==> ./configure --prefix=/usr/local/Cellar/python3/3.3.0 --enable-ipv6 --datarootdir=/usr/local/Cell
==> make
==> make install PYTHONAPPSDIR=/usr/local/Cellar/python3/3.3.0
==> make frameworkinstallextras PYTHONAPPSDIR=/usr/local/Cellar/python3/3.3.0/share/python3
==> Downloading https://pypi.python.org/packages/source/d/distribute/distribute-0.6.35.tar.gz
Already downloaded: /Library/Caches/Homebrew/distribute-0.6.35.tar.gz
==> /usr/local/Cellar/python3/3.3.0/bin/python3.3 -s setup.py install --force --verbose --install-li
==> Downloading https://pypi.python.org/packages/source/p/pip/pip-1.3.1.tar.gz
Already downloaded: /Library/Caches/Homebrew/pip-1.3.1.tar.gz
==> /usr/local/Cellar/python3/3.3.0/bin/python3.3 -s setup.py install --force --verbose --install-li
==> Caveats
Homebrew's Python3 framework
  /usr/local/Cellar/python3/3.3.0/Frameworks/Python.framework

Distribute and Pip have been installed. To update them
  pip3 install --upgrade distribute
  pip3 install --upgrade pip

To symlink "Idle 3" and the "Python Launcher 3" to ~/Applications
  `brew linkapps`

You can install Python packages with
  `pip3 install <your_favorite_package>`

They will install into the site-package directory
 /usr/local/lib/python3.3/site-packages
Executable python scripts will be put in:
 /usr/local/share/python3
so you may want to put "/usr/local/share/python3" in your PATH, too.

See: https://github.com/mxcl/homebrew/wiki/Homebrew-and-Python

Once installed update your system PATH variable, add the next line to ~/.bash_profile

export PATH=/usr/local/bin:/usr/local/sbin:~/bin:$PATH

And then:

$ source ~/.bash_profile

Now launch Python:

$ python3
Python 3.3.0 (default, Mar 26 2013, 10:01:40) 
[GCC 4.2.1 Compatible Apple LLVM 4.2 (clang-425.0.27)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>

You can check python3 path:

$ which python3
/usr/local/bin/python3

Find path of Python installed by Homebrew

Use brew info <packagename>

it's probably in one of (and referenced in both)

/usr/local/Cellar/python@3.8/3.8.6_2
/usr/local/opt/python@3.8/libexec/bin

See also Apple SE Where can I find the installed package path via brew

If it's not there, it's plausible the version detection is wrong and only searches for the first two version digits (as conflicting versions may clobber each other). In this case, follow the warning and reinstall the specific version you want.