python/cpython · error · ValueError

Don't know machine value for archs=%r

Error message

Don't know machine value for archs=%r

What it means

Raised in _osx_support while normalizing the macOS machine/platform name from the ARCHFLAGS architecture list. Only a fixed table of architecture tuples maps to a machine value — ('arm64','x86_64') -> universal2, ('i386','ppc') -> fat, ('i386','x86_64') -> intel, ('i386','ppc','x86_64') -> fat3, ('ppc64','x86_64') -> fat64, ('i386','ppc','ppc64','x86_64') -> universal. Any other combination raises ValueError('Don't know machine value for archs=%r'). It guards against unsupported universal-build architecture sets.

Source

Thrown at Lib/_osx_support.py:562

            archs = re.findall(r'-arch\s+(\S+)', cflags)
            archs = tuple(sorted(set(archs)))

            if len(archs) == 1:
                machine = archs[0]
            elif archs == ('arm64', 'x86_64'):
                machine = 'universal2'
            elif archs == ('i386', 'ppc'):
                machine = 'fat'
            elif archs == ('i386', 'x86_64'):
                machine = 'intel'
            elif archs == ('i386', 'ppc', 'x86_64'):
                machine = 'fat3'
            elif archs == ('ppc64', 'x86_64'):
                machine = 'fat64'
            elif archs == ('i386', 'ppc', 'ppc64', 'x86_64'):
                machine = 'universal'
            else:
                raise ValueError(
                   "Don't know machine value for archs=%r" % (archs,))

        elif machine == 'i386':
            # On OSX the machine type returned by uname is always the
            # 32-bit variant, even if the executable architecture is
            # the 64-bit variant
            if sys.maxsize >= 2**32:
                machine = 'x86_64'

        elif machine in ('PowerPC', 'Power_Macintosh'):
            # Pick a sane name for the PPC architecture.
            # See 'i386' case
            if sys.maxsize >= 2**32:
                machine = 'ppc64'
            else:
                machine = 'ppc'

    return (osname, release, machine)

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Unset ARCHFLAGS and let the build use the interpreter's defaults: `unset ARCHFLAGS`
2. If you must pin arches, use a supported set: ARCHFLAGS='-arch arm64 -arch x86_64' (universal2) or a single '-arch arm64' / '-arch x86_64'
3. Check for stray whitespace/duplicates/order variations in ARCHFLAGS and normalize the tuple
4. Upgrade setuptools/pip so platform detection uses current macOS logic instead of stale vendored copies

Example fix

# before
export ARCHFLAGS='-arch i386 -arch ppc -arch arm64'   # ValueError

# after
unset ARCHFLAGS
# or a supported combination:
export ARCHFLAGS='-arch arm64 -arch x86_64'

SUPPORTED = {
    ('arm64', 'x86_64'), ('i386', 'ppc'), ('i386', 'x86_64'),
    ('i386', 'ppc', 'x86_64'), ('ppc64', 'x86_64'),
    ('i386', 'ppc', 'ppc64', 'x86_64'),
}

def validate_archflags(archflags: str) -> None:
    import shlex
    archs = tuple(a for a in shlex.split(archflags) if a == '-arch') and tuple(
        shlex.split(archflags)[i + 1] for i, a in enumerate(shlex.split(archflags)) if a == '-arch'
    ) or ()
    if archs and archs not in SUPPORTED:
        raise ValueError(f'Unsupported ARCHFLAGS arch set {archs}; use e.g. arm64+x86_64 or unset ARCHFLAGS')

When it happens

Trigger: Setting the ARCHFLAGS environment variable to an architecture combination outside the supported table — e.g. ARCHFLAGS='-arch ppc -arch arm64', a single legacy arch like '-arch ppc7400', or a reordered/duplicated set like 'arm64 arm64 x86_64' — then triggering platform/compiler customization (building extensions, sysconfig.get_platform() on macOS).

Common situations: ARCHFLAGS copied from old build docs or a Linux CI script; cross-compile experiments mixing ppc with modern arm64; fat-binary instructions from the PowerPC era; ARCHFLAGS inherited from a shell profile across macOS upgrades; single-arch values that don't hit the x86_64 default path.

Related errors

• Cannot locate working compiler
• Python ssl module is not available
• posix_spawnattr_setbinpref failed to copy\n
• terminal doesn't have the required {cap} capability
• stdlib ssl module not available

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/2eebe3ec7a3f78bd. Report an issue: GitHub.