`make install` fails in `ensurepip` if zlib extension is missing

[Andrej730]

Bug report

Bug description:

Compilation without zlib worked fine, but installation fails with ModuleNotFoundError: No module named 'zlib'.
So is this dependency not actually optional?

# make -j8
./python -E ../Tools/build/generate-build-details.py `cat pybuilddir.txt`/build-details.json
The following modules are *disabled* in configure script:
_sqlite3

The necessary bits to build these optional modules were not found:
_bz2                  _ctypes               _ctypes_test
_curses               _curses_panel         _dbm
_gdbm                 _lzma                 _tkinter
_uuid                 _zstd                 readline
zlib
To find the necessary bits, look in configure.ac and config.log.

Installation:

# make install
(cd /python-install/share/man/man1; ln -s python3.14.1 python3.1)
if test "xupgrade" != "xno"  ; then \
        case upgrade in \
                upgrade) ensurepip="--upgrade" ;; \
                install|*) ensurepip="" ;; \
        esac; \
         ./python -E -m ensurepip \
                $ensurepip --root=/ ; \
fi
Traceback (most recent call last):
  File "<frozen zipimport>", line 620, in _get_decompress_func
ModuleNotFoundError: No module named 'zlib'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<frozen zipimport>", line 668, in _get_data
  File "<frozen zipimport>", line 623, in _get_decompress_func
zipimport.ZipImportError: can't decompress data; zlib not available

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<string>", line 6, in <module>
    runpy.run_module("pip", run_name="__main__", alter_sys=True)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen runpy>", line 222, in run_module
  File "<frozen runpy>", line 148, in _get_module_details
  File "<frozen runpy>", line 112, in _get_module_details
  File "<frozen zipimport>", line 136, in get_code
  File "<frozen zipimport>", line 802, in _get_module_code
  File "<frozen zipimport>", line 670, in _get_data
zipimport.ZipImportError: can't decompress data; zlib not available
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/Python-3.14.0/Lib/ensurepip/__main__.py", line 5, in <module>
    sys.exit(ensurepip._main())
             ~~~~~~~~~~~~~~~^^
  File "/Python-3.14.0/Lib/ensurepip/__init__.py", line 257, in _main
    return _bootstrap(
        root=args.root,
    ...<4 lines>...
        default_pip=args.default_pip,
    )
  File "/Python-3.14.0/Lib/ensurepip/__init__.py", line 172, in _bootstrap
    return _run_pip([*args, "pip"], [os.fsdecode(tmp_wheel_path)])
  File "/Python-3.14.0/Lib/ensurepip/__init__.py", line 87, in _run_pip
    return subprocess.run(cmd, check=True).returncode
           ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/Python-3.14.0/Lib/subprocess.py", line 577, in run
    raise CalledProcessError(retcode, process.args,
                             output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['/Python-3.14.0/build/python', '-W', 'ignore::DeprecationWarning', '-c', '\nimport runpy\nimport sys\nsys.path = [\'/tmp/tmpe4cza5y6/pip-25.2-py3-none-any.whl\'] + sys.path\nsys.argv[1:] = [\'install\', \'--no-cache-dir\', \'--no-index\', \'--find-links\', \'/tmp/tmpe4cza5y6\', \'--root\', \'/\', \'--upgrade\', \'pip\']\nrunpy.run_module("pip", run_name="__main__", alter_sys=True)\n']' returned non-zero exit status 1.
make: *** [Makefile:2496: install] Error 1

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-139823: Extend list of optional dependencies in configure.rst #139826
• [3.14] gh-139823: Extend list of optional dependencies in configure.rst (GH-139826) #139887
• gh-139823: Check if zlib is available in ensurepip #139954

[StanFromIreland]

See PEP 775 :-)

Note that it built fine, just pip cannot be installed.

CC @encukou

[encukou]

Improvements to docs and/or error messages are welcome!
I'm putting this on my TODO list, but feel free to beat me to it :)

[StanFromIreland]

We could try import zlib in ensurepip and exit with a nicer error message if it is not found?