Python installation on ARM64 doesn't work on M3

[izycheva]

I wanted to try the fix for the earlier issue, where I was advised to upgrade to the latest version of Z3 4.16.0, but seems like the wheel for z3-solver on arm64 is not the right one.

I have a Macbook with M3, I tried a fresh venv with explicit arm configuration and it installs successfully, but then I cannot import the module.

$ arch -arm64 python3 -m venv ~/.arm 
$ source ~/.arm/bin/activate
(.arm) $ arch -arm64 pip install z3-solver -U 
Collecting z3-solver
  Using cached z3_solver-4.16.0.0.tar.gz (5.1 MB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
  Preparing metadata (pyproject.toml) ... done
Building wheels for collected packages: z3-solver
  Building wheel for z3-solver (pyproject.toml) ... done
  Created wheel for z3-solver: filename=z3_solver-4.16.0.0-py3-none-macosx_14_6_arm64.whl size=35138697 sha256=5204c7e82d088fb0386c4a8672dab4de3f2cc2db2f4f0f2f77189ff88168fa72
  Stored in directory: /Users/anastasia/Library/Caches/pip/wheels/53/bb/e4/ebed8621a4c2ec01d8a1e6423fb976b2b5374e84fc99012f1a
Successfully built z3-solver
Installing collected packages: z3-solver
Successfully installed z3-solver-4.16.0.0

[notice] A new release of pip is available: 25.2 -> 26.0.1
[notice] To update, run: pip install --upgrade pip

Using the module:

(.arm) $ python
Python 3.14.0 (v3.14.0:ebf955df7a8, Oct  7 2025, 08:20:14) [Clang 16.0.0 (clang-1600.0.26.6)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import z3
Could not find libz3.dylib; consider adding the directory containing it to
  - your system's PATH environment variable,
  - the Z3_LIBRARY_PATH environment variable, or 
  - to the custom Z3_LIB_DIRS Python-builtin before importing the z3 module, e.g. via
    import builtins
    builtins.Z3_LIB_DIRS = [ '/path/to/z3/lib/dir' ] # directory containing libz3.dylib
[OSError("dlopen(/Users/anastasia/.arm/lib/python3.14/site-packages/z3/lib/libz3.dylib, 0x0006): tried: '/Users/anastasia/.arm/lib/python3.14/site-packages/z3/lib/libz3.dylib' (mach-o file, but is an incompatible architecture (have 'x86_64', need 'arm64e' or 'arm64')), '/System/Volumes/Preboot/Cryptexes/OS/Users/anastasia/.arm/lib/python3.14/site-packages/z3/lib/libz3.dylib' (no such file), '/Users/anastasia/.arm/lib/python3.14/site-packages/z3/lib/libz3.dylib' (mach-o file, but is an incompatible architecture (have 'x86_64', need 'arm64e' or 'arm64'))"), TypeError('expected str, bytes or os.PathLike object, not NoneType'), OSError("dlopen(libz3.dylib, 0x0006): tried: 'libz3.dylib' (no such file), '/System/Volumes/Preboot/Cryptexes/OSlibz3.dylib' (no such file), '/usr/lib/libz3.dylib' (no such file, not in dyld cache), 'libz3.dylib' (no such file)")]
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    import z3
  File "/Users/anastasia/.arm/lib/python3.14/site-packages/z3/__init__.py", line 1, in <module>
    from .z3 import *
  File "/Users/anastasia/.arm/lib/python3.14/site-packages/z3/z3.py", line 46, in <module>
    from . import z3core
  File "/Users/anastasia/.arm/lib/python3.14/site-packages/z3/z3core.py", line 79, in <module>
    raise Z3Exception("libz3.%s not found." % _ext)
z3.z3types.Z3Exception: libz3.dylib not found.

I also tried downloading the corresponding wheel from release page, but it doesn't seem to work either:

$ pip install z3_solver-4.16.0.0-py3-none-macosx_15_0_arm64.whl 
ERROR: z3_solver-4.16.0.0-py3-none-macosx_15_0_arm64.whl is not a supported wheel on this platform.

Is it possible that the linked file is not actually for arm64? Am I missing something?

[github-actions]

The error message is quite diagnostic: (mach-o file, but is an incompatible architecture (have 'x86_64', need 'arm64e' or 'arm64')). Even though you ran arch -arm64 pip install z3-solver, the bundled libz3.dylib inside the installed wheel is an x86_64 binary.

What's happening: The z3-solver source tarball (z3_solver-4.16.0.0.tar.gz) does not compile Z3 from scratch — it downloads a pre-built libz3.dylib from GitHub releases during the build. The download selection is based on the detected platform. If pip's build environment is running under Rosetta 2 (even when invoked with arch -arm64), the platform detection may select the x86_64 macOS binary.

Diagnostic steps:

1. Check your Python binary's architecture: file $(which python3) — if it shows x86_64 or universal binary executing as x86_64, that explains the download
2. Check if you're running under Rosetta: sysctl sysctl.proc_translated — 1 means Rosetta

Suggested workarounds:

1. Download the arm64 libz3.dylib directly from the Z3 4.16.0 release (look for z3-4.16.0-arm64-osx-*.zip) and set Z3_LIBRARY_PATH to point to it before importing
2. If the macOS 15 arm64 wheel fails with "not a supported wheel on this platform", it may be because your macOS 14 system does not match the macosx_15_0 compatibility tag. Try: pip install --platform macosx_14_0_arm64 --only-binary=:all: z3-solver (may require pip 22+)
3. Install Z3 via Homebrew (brew install z3) which will always produce a native arm64 binary, then set Z3_LIBRARY_PATH=$(brew --prefix z3)/lib

This appears related to #7687 (Python wheel architecture issues).

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[izycheva]

I have a universal binary and do not run under Rosetta:

$file $(which python3)
/Users/anastasia/.arm/bin/python3: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64:Mach-O 64-bit executable arm64]
/Users/anastasia/.arm/bin/python3 (for architecture x86_64):	Mach-O 64-bit executable x86_64
/Users/anastasia/.arm/bin/python3 (for architecture arm64):	Mach-O 64-bit executable arm64
$ sysctl sysctl.proc_translated
sysctl.proc_translated: 0

and if I check the platform inside python executable it is correctly identified as ARM:

Python 3.14.0 (v3.14.0:ebf955df7a8, Oct  7 2025, 08:20:14) [Clang 16.0.0 (clang-1600.0.26.6)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import platform
>>> platform.processor()
'arm'
>>> platform.machine()
'arm64'

I managed to install the library using pip install --platform macosx_15_0_arm64 --only-binary=:all: z3-solver -U --target /Users/anastasiia/.arm/lib/python3.14/site-packages/z3/ -U, but this library is not visible under pip list, and a simple test fails:

Python 3.14.0 (v3.14.0:ebf955df7a8, Oct  7 2025, 08:20:14) [Clang 16.0.0 (clang-1600.0.26.6)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import z3
>>> s = z3.Solver()
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    s = z3.Solver()
        ^^^^^^^^^
AttributeError: module 'z3' has no attribute 'Solver'