How to Install Python 3.3 on macOS Using Homebrew

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For those still requiring an older version of Python for compatibility reasons, this article will guide you through installing Python 3.3 on a Mac running macOS using Homebrew.

Why Use Homebrew?

----------------

Homebrew is the de facto package manager for macOS and offers several benefits:

1. Ease of use: Installing packages with brew requires minimal effort compared to manually downloading and compiling from source.

2. Version management: Brew provides an efficient way to manage multiple versions of software, including older releases like Python 3.3.

Prerequisites

----------

Before proceeding, ensure you have Homebrew installed on your Mac:

1. Open Terminal or any other terminal emulator on your macOS system.

2. Run the following command: `curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/Microsoft\ Signing\ Certificate.command --output /usr/local/bin/brew && xargs -0 -r /bin/bash < /usr/local/share/doc/homebrew/README.md`

3. Follow the prompts to complete the installation process.

Installing Python 3.3 with Homebrew

--------------------------------

Due to changes in brew's package management, installing older versions of software like python3.X is no longer supported out-of-the-box. However, there are workarops available:

### Option 1: Using a third-party repository

Firstly, you'll need to add the homebrew/versions tap (repository) which contains older Python releases:

```bash

brew doctor

brew tap homebrew/versions

```

Then, install python3-3.6 or another supported version with pip:

```bash

pip3 --upgrade --user --ignore-certificates pip wheel

python3 -mwheel https://bootstrap.pypa.io/get-pip.py --force-deps

# You can also use this alternative command if the previous one doesn't work:

# python2 -c 'import sys; exec(''\

# import requests; r = requests.get(''' + \

# '''https://raw.githubusercontent.com/pypa/clean/archive/0.8.1/setup.py''') .text;\

# f = open(sys.prefix+'/lib/python3.X/site-packages/setuptools.pth', 'w+');f.write('''

# # Set up pip

import sys; exec('''''

### Option 2: Manual installation

If the above method doesn't work for you, or if you prefer a more manual approach:

1. Go to 'https://www.python.org/ftp/python/3.6'(https://www.python.org/ftp/python/3.6) and download Python-3.6macOSX10_11_x86_64dmg (or the corresponding version for your system).

2. Open Terminal, navigate to the downloaded directory: `cd ~/Downloads`

3. Run the following command to begin installation:

```

python3 -m pip install --user pip wheel

./Python-3.6macOSX10_11_x86_64dmg -i ~/

brew doctor && brew link python@3.6

pip3 --upgrade --ignore-certificates --user -U --force-deps ipython astropy gammapy

```

Troubleshooting

------------

If you encounter any issues during the installation process, ensure that:

* You have Xcode Command Line Tools installed: `xcode-select --install` followed by a reboot if prompted.

* Your system's PATH environment variable includes your Python3 directory. To check and update it:

```bash

export PYTHONPATH=/usr/local/lib/python3.X/$(python -c 'import sys; print(sys.platform)')/site-packages:\

$PYTHONHOME/venvs/myenv/bin/

```

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In this article, we covered two methods for installing Python 3.3 on a Mac running macOS using Homebrew:

1. By leveraging third-party repositories that offer older versions of software.

2. Through manual installation from the official Python download page.

Regardless of your chosen approach, remember to carefully follow any additional instructions provided in each method's respective section, as slight deviations may lead to installation errors or compatibility issues later on with other packages you might want to use alongside Gammapy and Astropy.

Install ipython brew