ImportError: Symbol not found: ___chkstk_darwin

The prebuilt curlcffi wheel was compiled for a newer macOS than yours, and the old system's loader cannot resolve `chkstkdarwin. Upgrade curl_cffi (python -m pip install -U curl_cffi`) to a release whose wheels cover your macOS version. If no wheel covers it, the fallback is upgrading macOS itself.

The error

ImportError: dlopen([path]/curl_cffi/requests/libs/wrapper.abi3.so, 0x0002): Symbol not found: ___chkstk_darwin

Fix it

1. Check your macOS and curl_cffi versions

sw_vers -productVersion
python -m pip show curl_cffi | head -2

Expected: an older macOS (10.15-era reports cluster here) with an older curl_cffi.

1. Upgrade curl_cffi

python -m pip install -U curl_cffi

Expected: a newer wheel whose minimum macOS matches yours. Re-run the import.

1. Confirm

python -c "from curl_cffi import Session; print('ok')"

Expected: prints ok with no dlopen error.

When this applies

• the ImportError names ___chkstk_darwin on macOS
• the traceback shows a dlopen of curl_cffi's bundled .so
• an older Mac that cannot take the newest macOS

When it does NOT apply

• Linux undefined symbol errors are the Linux cousin (different symbol, usually a glibc mismatch)
• No module named 'curl_cffi' is the missing install

Compatibility

Reported against older curl_cffi wheels on macOS 10.15 and similar. Newer wheels raised the floor or fixed the symbol usage.

Why it happens

___chkstk_darwin is a compiler helper for stack probing on macOS. Wheels built with a newer SDK targeting newer macOS emit references to it, and the dynamic loader on older macOS has no such symbol, so dlopen fails. It is a build-floor problem: the wheel promises an older macOS than its code actually supports.

Edge cases

• Rosetta vs native rarely matters here; the symbol issue is about the macOS version, not the arch.
• If upgrading is truly impossible, building curl_cffi from source on the old Mac produces a binary matching that system. It needs a compiler and the curl dev headers.
• Do not downgrade Python to dodge this. The symbol comes from the wheel's C code, not the interpreter.