How can I install a previous version of Python 3 in macOS using homebrew?

To solve this with homebrew, you can temporarily backdate homebrew-core and set the HOMEBREW_NO_AUTO_UPDATE variable to hold it in place:

cd `brew --repo homebrew/core`
git checkout f2a764ef944b1080be64bd88dca9a1d80130c558
export HOMEBREW_NO_AUTO_UPDATE=1
brew install python

I don’t recommend permanently backdating homebrew-core, as you will miss out on security patches, but it is useful for testing purposes.

You can also extract old versions of homebrew formulae into your own tap (tap_owner/tap_name) using the brew extract command:

brew extract python tap_owner/tap_name --version=3.6.5

As an update, when doing

brew unlink python # If you have installed (with brew) another version of python
brew install https://raw.githubusercontent.com/Homebrew/homebrew-core/f2a764ef944b1080be64bd88dca9a1d80130c558/Formula/python.rb

You may encounter

Error: python contains a recursive dependency on itself:
  python depends on sphinx-doc
  sphinx-doc depends on python

To bypass it, add the --ignore-dependencies argument to brew install.

brew unlink python # If you have installed (with brew) another version of python
brew install --ignore-dependencies https://raw.githubusercontent.com/Homebrew/homebrew-core/f2a764ef944b1080be64bd88dca9a1d80130c558/Formula/python.rb

What I did was first I installed python 3.7 and then unlinked it using the following commands

brew install python3
brew unlink python

then I installed python 3.6.5 using the following command taken from above answer.

brew install --ignore-dependencies https://raw.githubusercontent.com/Homebrew/homebrew-core/f2a764ef944b1080be64bd88dca9a1d80130c558/Formula/python.rb --ignore-dependencies

After that I ran the following command

brew link --overwrite python

Now I have all pythons in the system. To find out run

mian@tdowrick2~ $ python --version
Python 2.7.10
mian@tdowrick2~ $ python3.7 --version
Python 3.7.1
mian@tdowrick2~ $ python3.6 --version
Python 3.6.5

To create Python 3.7 virtual environment.

mian@tdowrick2~ $ virtualenv -p python3.7 env
Already using interpreter /Library/Frameworks/Python.framework/Versions/3.7/bin/python3.7
Using base prefix '/Library/Frameworks/Python.framework/Versions/3.7'
New python executable in /Users/mian/env/bin/python3.7
Also creating executable in /Users/mian/env/bin/python
Installing setuptools, pip, wheel...
done.
mian@tdowrick2~ $ source env/bin/activate
(env) mian@tdowrick2~ $ python --version
Python 3.7.1
(env) mian@tdowrick2~ $ deactivate

To create Python 3.6 virtual environment

mian@tdowrick2~ $ virtualenv -p python3.6 env
Running virtualenv with interpreter /usr/local/bin/python3.6
Using base prefix '/usr/local/Cellar/python/3.6.5_1/Frameworks/Python.framework/Versions/3.6'
New python executable in /Users/mian/env/bin/python3.6
Not overwriting existing python script /Users/mian/env/bin/python (you must use /Users/mian/env/bin/python3.6)
Installing setuptools, pip, wheel...
done.
mian@tdowrick2~ $ source env/bin/activate
(env) mian@tdowrick2~ $ python --version
Python 3.6.5
(env) mian@tdowrick2~ $ deactivate

I tried all the answers above to install Python 3.4.4. The installation of python worked, but PIP would not be installed and nothing I could do to make it work. I was using Mac OSX Mojave, which cause some issues with zlib, openssl.

What not to do:

• Try to avoid using Homebrew for previous version given by the formula Python or Python3.
• Do not try to compile Python

Solution:

1. Download the macOS 64-bit installer or macOS 64-bit/32-bit installer: https://www.python.org/downloads/release/python-365/
2. In previous step, it will download Python 3.6.5, if for example, you want to download Python 3.4.4, replace in the url above python-365 by python-344
3. Download click on the file you downloaded a GUI installer will open
4. If you downloaded python-365, after installation, to launch this version of python, you will type in your terminal python365, same thing for pip, it will be pip365

p.s: You don’t have to uninstall your other version of Python on your system.

Edit:

I found a much much much better solution that work on MacOSX, Windows, Linux, etc.

1. It doesn’t matter if you have already python installed or not.
2. Download Anaconda
3. Once installed, in terminal type: conda init
4. In terminal,create virtual environment with any python version, for example, I picked 3.4.4: conda create -n [NameOfYour VirtualEnvironment] python=3.4.4
5. Then, in terminal, you can check all the virtual environment you ahave created with the command: conda info --envs
6. Then, in terminal, activate the virtual environment of your choice with: conda activate [The name of your virtual environment that was shown with the command at step 5]

I have tried everything but could not make it work. Finally I have used pyenv and it worked directly like a charm.

So having homebrew installed, juste do:

brew install pyenv
pyenv install 3.6.5

to manage virtualenvs:

brew install pyenv-virtualenv
pyenv virtualenv 3.6.5 env_name

See pyenv and pyenv-virtualenv for more info.

EDIT (2020/03/19)

I have found using the pyenv-installer easier than homebrew to install pyenv and pyenv-virtualenv direclty:

curl https://pyenv.run | bash

To manage python version, either globally:

pyenv global 3.6.5

or locally in a given directory:

pyenv local 3.6.5

In case anyone face pip issue like below

pip is configured with locations that require TLS/SSL, however the ssl module in Python is not available.

The root cause is openssl 1.1 doesn’t support python 3.6 anymore. So you need to install old version openssl 1.0

here is the solution:

brew uninstall --ignore-dependencies openssl
brew install https://github.com/tebelorg/Tump/releases/download/v1.0.0/openssl.rb

The easiest way for me was to install Anaconda: https://docs.anaconda.com/anaconda/install/

There I can create as many environments with different Python versions as I want and switch between them with a mouse click. It could not be easier.

To install different Python versions just follow these instructions https://docs.conda.io/projects/conda/en/latest/user-guide/tasks/manage-python.html

A new development environment with a different Python version was done within 2 minutes. And in the future I can easily switch back and forth.