- You are using Python on macOS M1 (or M2, etc) and are trying to install a Python library which uses a native library.
- You install the Python library (e.g. using
pip) and the native library (using Homebrew). - You get an error saying that the native library cannot be located even though it's installed using Homebrew.
Example: You are trying to use e.g. pyfluidsynth. You've installed pyfluidsynth with pip, and also ran brew install fluidsynth. However, import fluidsynth still gives an error:
ImportError: Couldn't find the FluidSynth library.
What happens is that pyfluidsynth uses ctypes.find_library to locate the native fluidsynth library.
However, find_library doesn't find libraries installed by Homebrew on M1 because Homebrew installs libraries
in /opt/homebrew/lib (instead of /usr/local/bin used for Intel Macs) which is not in the default library search path.
In order to solve this, you must tell Python to look in /opt/homebrew/lib. Use any of the following solutions depending on your setup. If you are using pyenv, jump straight to solution 3.
Use Python installed by Homebrew (brew install python).
Homebrew patches ctypes itself
in their version of Python, so that native libraries installed using Homebrew are found by find_library.
This solution won't work if you want to use pyenv or any other installation of Python. It will only work with Homebrew-installed Python. You can apply the same patch to your own installation of Python, but if you use pyenv and multiple versions of Python this becomes quite annoying.
You can set an environment variable that will make ctypes.find_library look in Homebrew's library path:
export DYLD_FALLBACK_LIBRARY_PATH="/opt/homebrew/lib:$DYLD_FALLBACK_LIBRARY_PATH"You can add this line to your shell profile (~/.zprofile) so that it happens in every shell. Restart your shell for the changes to take effect.
This solution still won't work if you use pyenv.
Why? Because of a macOS security feature called SIP which prevents the variable
DYLD_FALLBACK_LIBRARY_PATH
from being forwarded to 'protected processes' such as the shell. And since pyenv uses a shell script to start Python, it won't get the new DYLD_FALLBACK_LIBRARY_PATH. You may be able to bypass this by partially disabling SIP in Recovery Mode.
Python executes a script called usercustomize every time it starts up. We can use that to make sure DYLD_FALLBACK_LIBRARY_PATH is set correctly in every Python process. We can even do that for all installed Python versions in a single place. And it works even with pyenv.
Create a usercustomize.py file: ~/.local/lib/global-packages/usercustomize.py. Paste in it the following script:
import os
homebrew_lib_dir = "/opt/homebrew/lib"
existing_lib_path = os.environ.get("DYLD_FALLBACK_LIBRARY_PATH", "")
os.environ["DYLD_FALLBACK_LIBRARY_PATH"] = homebrew_lib_dir + ":" + existing_lib_pathThen, make this usercustomize script be used by any Python interpreter (regardless of version): In your ~/.zprofile add the following line:
export PYTHONPATH="$HOME/.local/lib/global-packages:$PYTHONPATH"