Homebrew provides formulae to brew Python 3.x. Homebrew provided a python@2 formula until the end of 2019, at which point it was removed due to the Python 2 deprecation. Important: If you choose to use a Python which isn’t either of these two (system Python or brewed Python), the Homebrew team cannot support any breakage that may occur. MacOS 10.14 (Mojave and Catalina) Python 3.6 and Python 3.7 are supported. Note that Python 3.8 is not supported at this point. Python 2.7 is not supported, since the Python 2 End-Of-Life happened at the start of 2020.
I'm still working on getting pyenv in my bloodstream. It seems like totally the right tool for having different versions of Python available on macOS that don't suddenly break when you run brew upgrade periodically. But every thing I tried failed with an error similar to this:
I read through the Troubleshooting FAQ and the 'Common build problems' documentation. xcode was up to date and I had all the related brew packages upgraded. Nothing seemed to work.
Until I saw this comment on an open pyenv issue: 'Unable to install any Python version on MacOS'
All I had to do was replace the 10.14 for 10.15 and now it finally worked here on Catalina 10.15. So, the magical line was this:
Hopefully, by blogging about it you'll find this from Googling and I'll remember the next time I need it because it did eat 2 hours of precious evening coding time.
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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
As Apple has announced, Mac OS Catalina now runs under its own read only file system:
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:
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:
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
To understand this more fully, take a look at https://stackoverflow.com/questions/18783390/python-pip-specify-a-library-directory-and-an-include-directory.
Catalina Python3 Install
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.
Catalina Python3 Pip
[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