Python not working, /usr/lib/libexpat.1.dylib missing (macOS: 26.2-arm64)

[glensc]

Output of brew config

HOMEBREW_VERSION: 5.1.6
ORIGIN: https://github.com/Homebrew/brew
HEAD: 299ab19496df6fc76e8356c0b87100ff91ef827e
Last commit: 24 hours ago
Branch: stable
Core tap JSON: 14 Apr 11:55 UTC
Core cask tap JSON: 14 Apr 11:55 UTC
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_CASK_OPTS: []
HOMEBREW_DOWNLOAD_CONCURRENCY: 28
HOMEBREW_EDITOR: vim
HOMEBREW_FORBID_PACKAGES_FROM_PATHS: set
HOMEBREW_GITHUB_API_TOKEN: set
HOMEBREW_MAKE_JOBS: 14
Homebrew Ruby: 4.0.2 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/4.0.2_1/bin/ruby
CPU: 14-core 64-bit arm_brava
Clang: 17.0.0 build 1700
Git: 2.50.1 => /Library/Developer/CommandLineTools/usr/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 26.2-arm64
CLT: 26.3.0.0.1.1771626560
Xcode: N/A
Rosetta 2: false

Output of brew doctor

Please note that these warnings are just used to help the Homebrew maintainers
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Warning: Some installed casks are deprecated or disabled.
You should find replacements for the following casks:
  rar

Warning: Some installed kegs have no formulae!
This means they were either deleted or installed manually.
You should find replacements for the following formulae:
  terraform

Warning: Some installed formulae are deprecated or disabled.
You should find replacements for the following formulae:
  icu4c@77
  node@20
  terraform

Warning: Putting non-prefixed coreutils in your path can cause GMP builds to fail.

Warning: Putting non-prefixed findutils in your path can cause python builds to fail.

Description of issue

Python stopped working, more particular awscli, and then also pip. I tried to pip reinstall awscli, python@3.14, also tried python@3.13, they all end up with error like this:

$ python3 --version
Python 3.14.4

$ python3 -m pip install awscli
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/opt/homebrew/lib/python3.14/site-packages/pip/__main__.py", line 24, in <module>
    sys.exit(_main())
             ~~~~~^^
  File "/opt/homebrew/lib/python3.14/site-packages/pip/_internal/cli/main.py", line 83, in main
    command = create_command(cmd_name, isolated=("--isolated" in cmd_args))
  File "/opt/homebrew/lib/python3.14/site-packages/pip/_internal/commands/__init__.py", line 121, in create_command
    module = importlib.import_module(module_path)
  File "/opt/homebrew/Cellar/python@3.14/3.14.4/Frameworks/Python.framework/Versions/3.14/lib/python3.14/importlib/__init__.py", line 88, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap>", line 1406, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1371, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1342, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 938, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 759, in exec_module
  File "<frozen importlib._bootstrap>", line 491, in _call_with_frames_removed
  File "/opt/homebrew/lib/python3.14/site-packages/pip/_internal/commands/install.py", line 22, in <module>
    import pip._internal.self_outdated_check  # noqa: F401
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/lib/python3.14/site-packages/pip/_internal/self_outdated_check.py", line 21, in <module>
    from pip._internal.index.package_finder import PackageFinder
  File "/opt/homebrew/lib/python3.14/site-packages/pip/_internal/index/package_finder.py", line 42, in <module>
    from pip._internal.req import InstallRequirement
  File "/opt/homebrew/lib/python3.14/site-packages/pip/_internal/req/__init__.py", line 12, in <module>
    from .req_install import InstallRequirement
  File "/opt/homebrew/lib/python3.14/site-packages/pip/_internal/req/req_install.py", line 37, in <module>
    from pip._internal.operations.install.wheel import install_wheel
  File "/opt/homebrew/lib/python3.14/site-packages/pip/_internal/operations/install/wheel.py", line 33, in <module>
    from pip._vendor.distlib.scripts import ScriptMaker
  File "/opt/homebrew/lib/python3.14/site-packages/pip/_vendor/distlib/scripts.py", line 16, in <module>
    from .compat import sysconfig, detect_encoding, ZipFile
  File "/opt/homebrew/lib/python3.14/site-packages/pip/_vendor/distlib/compat.py", line 81, in <module>
    import xmlrpc.client as xmlrpclib
  File "/opt/homebrew/Cellar/python@3.14/3.14.4/Frameworks/Python.framework/Versions/3.14/lib/python3.14/xmlrpc/client.py", line 138, in <module>
    from xml.parsers import expat
  File "/opt/homebrew/Cellar/python@3.14/3.14.4/Frameworks/Python.framework/Versions/3.14/lib/python3.14/xml/parsers/expat.py", line 4, in <module>
    from pyexpat import *
ImportError: dlopen(/opt/homebrew/Cellar/python@3.14/3.14.4/Frameworks/Python.framework/Versions/3.14/lib/python3.14/lib-dynload/pyexpat.cpython-314-darwin.so, 0x0002): Symbol not found: _XML_SetAllocTrackerActivationThreshold
  Referenced from: <1AAB1AFF-0B6A-3B67-86F5-A72CB69F8B1B> /opt/homebrew/Cellar/python@3.14/3.14.4/Frameworks/Python.framework/Versions/3.14/lib/python3.14/lib-dynload/pyexpat.cpython-314-darwin.so
  Expected in:     <4D62FA9D-D86A-3DD0-98F2-C6D0718849E8> /usr/lib/libexpat.1.dylib

The expat library is just not there:

$ ls -ld /usr/lib/libexpat.1.dylib
ls: cannot access '/usr/lib/libexpat.1.dylib': No such file or directory
$ ls -ld /usr/lib/*expat*
zsh: no matches found: /usr/lib/*expat*

From the formula definition, the library should exist:

• https://github.com/Homebrew/homebrew-core/blob/ffac8630b0b01e7c476c4276cf936550304325b6/Formula/p/python%403.14.rb#L33

[cho-m]

You will need to upgrade to macOS 26.3 or later due to Apple upgrading their copy of expat.

[glensc]

But where is that libexpat.1.dylib residing? It's not in /usr/lib even after updating to 26.4.1.

What kind of sorcery is this?

[cho-m]

Apple uses a cache built into the OS so there is no physical file. Try running:

dyld_info /usr/lib/libexpat.dylib

[cody-elhard]

My Mac got bricked upgrading to 26.4 with a bad firmware update, so I'm waiting a bit

When trying to run aws-cli I get

...
ImportError: dlopen(/opt/homebrew/Cellar/python@3.14/3.14.4/Frameworks/Python.framework/Versions/3.14/lib/python3.14/lib-dynload/pyexpat.cpython-314-darwin.so, 0x0002): Symbol not found: _XML_SetAllocTrackerActivationThreshold
  Referenced from: <1AAB1AFF-0B6A-3B67-86F5-A72CB69F8B1B> /opt/homebrew/Cellar/python@3.14/3.14.4/Frameworks/Python.framework/Versions/3.14/lib/python3.14/lib-dynload/pyexpat.cpython-314-darwin.so
  Expected in:     <4D62FA9D-D86A-3DD0-98F2-C6D0718849E8> /usr/lib/libexpat.1.dylib

My short term hack

brew install expat
brew reinstall python@3.14
aws help # FAILS
DYLD_LIBRARY_PATH="/opt/homebrew/opt/expat/lib" aws help # WORKS

[Fewmanism]

Hitting the same error on macOS 26.2 (25C56) / Apple Silicon with python@3.14 3.14.5 (entry point was hermes-agent 2026.5.16, which transitively imports pyexpat via prompt_toolkit's HTML parser).

The install_name_tool workaround from #277330 still applies cleanly against the latest Homebrew expat (2.8.1):

brew install expat
install_name_tool -change /usr/lib/libexpat.1.dylib \
  "$(brew --prefix expat)/lib/libexpat.1.dylib" \
  /opt/homebrew/Cellar/python@3.14/3.14.5/Frameworks/Python.framework/Versions/3.14/lib/python3.14/lib-dynload/pyexpat.cpython-314-darwin.so
codesign --sign - --force \
  /opt/homebrew/Cellar/python@3.14/3.14.5/Frameworks/Python.framework/Versions/3.14/lib/python3.14/lib-dynload/pyexpat.cpython-314-darwin.so

Posting as another data point that the issue keeps biting 26.0–26.2 users who can't (yet) upgrade past 26.2. Would it be possible to either weak-link the new expat symbols in pyexpat, or ship an arm64_sequoia-style bottle as a fallback for pre-26.3 hosts, until 26.3+ adoption is broader?

[SMillerDev]

We're at 26.5 now and only the latest patch release of each major version is supported. If you make a pull request we will review it, but no promises on merging it