Install Python Mac Catalina

Pip broken under Mac OS X Catalina? TLDR;

pip install --global-option=build_ext --global-option='-I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/' --global-option='-L/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib/' --prefer-binary -r requirements.txt

On most versions of MacOS before Catalina, a distribution of Python is already included. Unfortunately, it’s almost certainly an old version, Python 2.7. Luckily, there are two ways to install Python 3 on a Mac with ease.
Install OpenCV 4 with Python 3 on macOS Catalina Posted on October 21, 2019 by Paul. Updated 11 February 2020. In this article, I will show you how to install OpenCV 4 with Python 3 on macOS Catalina.
The macOS 10.15 SDK provides support for developing apps for Macs running macOS Catalina 10.15. The SDK comes bundled with Xcode 11 available from the Mac App Store. For information on the compatibility requirements for Xcode 11, see Xcode 11 Release Notes.

As Apple has announced, Mac OS Catalina now runs under its own read only file system:

Install Python with NumPy, SciPy and Matplotlib on macOS Big Sur (Intel version) Posted on October 4, 2016 by Paul. Updated 15 June 2021. In this article, I will show you how to install Python with NumPy, SciPy and Matplotlib on macOS Big Sur. I assume you are on an Intel based Mac. The older Python language, version 2.7, is being deprecated in macOS 10.15 Catalina and won't be included in macOS 10.16. The same goes for other UNIX scripting languages.

macOS Catalina runs on a dedicated, read-only system volume called Macintosh HD. This volume is completely separate from all other data to help prevent the accidental overwriting of critical operating system files. [1]

Sounds great. But if you need to change that volume, or if you use software that expects to be able to find files on that read only volume that aren't there and can't be added, you're kind of stuck.

One example is Python's pip which, for some packages, will expect to find header files located in /usr/include. Apple gave developers a get-out-of-jail-free card in Mojave:

Install Python Mac Catalina Free

As a workaround, an extra package is provided which will install the headers to the base system. In a future release, this package will no longer be provided. [2]

and in true Apple fashion, the package was taken away. This creates problems if you want to install commonly used, but maybe not so commonly maintained, libraries. One example is Pillow, an image processing library. This will well and truly fail to compile if you just try pip install Pillow. It looks for the headers and libraries, and doesn't find them.

What can we do? Well, for pip there's a few options. The first is simply not to compile at all, but to prefer a binary. This is as simple in some cases as the --prefer-binary option. But what if, like Pillow, there is no precompiled binary for your platform? Or for reasons of information security, you have to compile it yourself?

Fortunately, pip can be directed to look in different places using the 'global-options' flag. To get Pillow to build, use the command at the top of this article, reproduced below:

Install Python Mac Catalina Operating System

To understand this more fully, take a look at https://stackoverflow.com/questions/18783390/python-pip-specify-a-library-directory-and-an-include-directory.

Install Python Mac Catalina Update

If you need to do a similar function as part of other install tools, common environment variables are LD_LIBRARY_PATH (deprecated[3], but still commonly used), LIBRARY_PATH and INCLUDE_PATH. Setting these to the library paths (/Library ... /usr/lib) and include paths (/Library ... /usr/include) respectively may help.

Install Python Mac Catalina Download

[1]https://support.apple.com/en-gb/HT210650
[2]https://developer.apple.com/documentation/xcode_release_notes/xcode_10_release_notes#3035624
[3]https://stackoverflow.com/questions/18241517/c-include-path-vs-ld-library-path