Use the shared libpython of conda-forge Pythons

conda-forge links the python executable statically, so sysconfig reports
LDLIBRARY=libpython3.X.a and Py_ENABLE_SHARED=0, but it ships
libpython3.X.so in LIBDIR too. The bridge now uses that library and
raises the error for a static Python only when there is none.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: ru551n

README.md

@@ -81,7 +81,7 @@ check(call_integer_vector("gain", arg(integer_vector'(1, 2))) = integer_vector'(
 - VUnit 5.0.0.dev12 or later (`vunit_hdl` on PyPI), which pip installs with the package.
 - VHDL-2008 or later.
 - CPython 3.10 or later, standard (GIL) build, with a shared `libpython` (`--enable-shared`), which
-  is what distribution Pythons, `actions/setup-python`, `uv` and `pyenv` provide by default.
+  is what distribution Pythons, `actions/setup-python`, `uv`, `pyenv` and conda-forge provide by default.
 - Linux and macOS: a C compiler (`cc`, `gcc` or `clang`, or `CC`) and the Python development headers
   (for example the `python3-dev` package). The bridge library is compiled on first use and cached.
 - Windows: a 64-bit CPython from python.org (or compatible). The package ships prebuilt DLLs

docs/requirements.rst

@@ -17,6 +17,8 @@ Requirements
   :ref:`python_bridge:native`. Python must provide a shared ``libpython``
   (``--enable-shared``), which is the case for distribution Pythons,
   ``actions/setup-python``, ``uv`` and ``pyenv`` builds with default settings.
+  conda-forge Pythons link the ``python`` executable statically but also
+  ship the shared library, which the bridge uses.
 * Windows: a 64-bit CPython from python.org (or compatible, such as
   ``actions/setup-python`` and ``uv``). No compiler is needed for NVC and GHDL
   when the package includes the prebuilt DLLs. Otherwise, and always for

release_notes/news.d/34.feature.md

@@ -0,0 +1 @@
+conda-forge Pythons are supported: their `python` executable links Python statically, but the bridge now uses the shared `libpython` they also ship.

src/vunit_python_bridge/native_library.py

@@ -229,16 +229,22 @@ def _python_library() -> Path:
 
     Regular --enable-shared builds name it in LDLIBRARY (libpython3.X.so, .dylib); macOS
     framework builds name the framework binary instead (Python.framework/Versions/3.X/Python).
+    conda-forge links its python executable statically but ships the shared library in LIBDIR too.
     """
     ldlibrary = sysconfig.get_config_var("LDLIBRARY") or ""
     framework = sysconfig.get_config_var("PYTHONFRAMEWORK") or ""
     version = f"{sys.version_info[0]}.{sys.version_info[1]}{getattr(sys, 'abiflags', '')}"
     shared = bool(sysconfig.get_config_var("Py_ENABLE_SHARED")) or bool(framework)
     if not shared or not (framework or ldlibrary.endswith((".so", ".dylib")) or ".so." in ldlibrary):
+        suffix = ".dylib" if sys.platform == "darwin" else ".so"
+        shared_library = Path(sysconfig.get_config_var("LIBDIR") or "") / f"libpython{version}{suffix}"
+        if shared_library.is_file():
+            return shared_library.resolve()
         raise PythonBridgeError(
             f"VHDL Python support requires a CPython built with a shared Python library (--enable-shared). "
             f"{sys.executable} links Python statically "
-            f"(LDLIBRARY={ldlibrary!r}, Py_ENABLE_SHARED={sysconfig.get_config_var('Py_ENABLE_SHARED')!r})."
+            f"(LDLIBRARY={ldlibrary!r}, Py_ENABLE_SHARED={sysconfig.get_config_var('Py_ENABLE_SHARED')!r}) "
+            f"and there is no {shared_library}."
         )
     prefix = Path(sys.base_prefix)
     candidates = [Path(sysconfig.get_config_var("LIBDIR") or "") / ldlibrary]

tests/test_python_bridge.py

@@ -725,7 +725,10 @@ def fake_get_paths():
             with self.assertRaisesRegex(RuntimeError, "Python.h"):
                 self._setup()
 
-    def test_static_only_python_raises(self):
+    def _static_python(self, libdir):
+        """
+        sysconfig of a statically linked Python with libdir as LIBDIR
+        """
         real_get_config_var = native_library.sysconfig.get_config_var
 
         def fake_get_config_var(name):
@@ -734,11 +737,28 @@ def fake_get_config_var(name):
                 return 0
             if name == "PYTHONFRAMEWORK":
                 return ""
+            if name == "LIBDIR":
+                return str(libdir)
             return real_get_config_var(name)
 
-        with mock.patch("vunit_python_bridge.native_library.sysconfig.get_config_var", side_effect=fake_get_config_var):
-            with self.assertRaisesRegex(RuntimeError, "shared Python library"):
-                self._setup()
+        return mock.patch.object(native_library.sysconfig, "get_config_var", side_effect=fake_get_config_var)
+
+    def test_static_only_python_raises(self):
+        libdir = self.tempdir / "static lib"
+        libdir.mkdir()
+        with self._static_python(libdir):
+            with self.assertRaisesRegex(RuntimeError, f"shared Python library.*no {re.escape(str(libdir))}"):
+                native_library._python_library()
+
+    def test_static_python_with_a_shared_library_uses_it(self):
+        # conda-forge: the python executable is static, LIBDIR has libpython3.X.so too
+        libdir = self.tempdir / "conda lib"
+        libdir.mkdir()
+        version = f"{sys.version_info[0]}.{sys.version_info[1]}{getattr(sys, 'abiflags', '')}"
+        library = libdir / f"libpython{version}{'.dylib' if sys.platform == 'darwin' else '.so'}"
+        library.write_bytes(b"")
+        with self._static_python(libdir):
+            self.assertEqual(native_library._python_library(), library.resolve())
 
     def test_free_threaded_python_raises(self):
         real_get_config_var = native_library.sysconfig.get_config_var