Hi folks,

Here’s a quick note on how to install Python 3.6 on MacOS 12 using pyenv.

I needed to do this while workingon a legacy app. Note that Python 3.6 has reached its end-of-life so you should normally be using a more recent version of the langauge as a developer.

Here is the error I was getting:

python-build: use readline from homebrew
Installing Python-3.6.0...
python-build: use tcl-tk from homebrew
python-build: use readline from homebrew
python-build: use zlib from xcode sdk

BUILD FAILED (OS X 12.0.1 using python-build 20180424)

Inspect or clean up the working tree at /var/folders/q9/s5s1hzrd6m1_0by3tx5j6sh40000gn/T/python-build.20220815235540.47954
Results logged to /var/folders/q9/s5s1hzrd6m1_0by3tx5j6sh40000gn/T/python-build.20220815235540.47954.log

Last 10 log lines:
clang -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include   -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include   -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers   -I. -I./Include -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/Users/olu/.pyenv/versions/3.6.0/openssl/include -I/Users/olu/.pyenv/versions/3.6.0/include  -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/Users/olu/.pyenv/versions/3.6.0/openssl/include -I/Users/olu/.pyenv/versions/3.6.0/include   -DPy_BUILD_CORE  -c ./Modules/pwdmodule.c -o Modules/pwdmodule.o
./Modules/posixmodule.c:8146:15: error: implicit declaration of function 'sendfile' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        ret = sendfile(in, out, offset, &sbytes, &sf, flags);
              ^
./Modules/posixmodule.c:10340:5: warning: code will never be executed [-Wunreachable-code]
    Py_FatalError("abort() called from Python code didn't abort!");
    ^~~~~~~~~~~~~
1 warning and 1 error generated.
make: *** [Modules/posixmodule.o] Error 1
make: *** Waiting for unfinished jobs....

After a lot of research, a solution was found on StackOverflow as follows:

CFLAGS="-I$(brew --prefix openssl)/include -I$(brew --prefix bzip2)/include -I$(brew --prefix readline)/include -I$(xcrun --show-sdk-path)/usr/include" 

LDFLAGS="-L$(brew --prefix openssl)/lib -L$(brew --prefix readline)/lib -L$(brew --prefix zlib)/lib -L$(brew --prefix bzip2)/lib"

pyenv install --patch 3.6.13 < <(curl -sSL https://github.com/python/cpython/commit/8ea6353.patch\?full_index\=1)

Hopefully this helps others. Till next time, happy software development.

References

1. Problems installing python 3.6 with pyenv on Mac OS Big Sur. https://stackoverflow.com/a/68227540.