build: allow a pure-Python wheel, and drop pkg_resources

Two changes that together let `vpython` be installed and imported under Pyodide/wasm. Both are opt-in or invisible to existing users: an ordinary `python -m build` still produces the same platform wheel it always did, and `install_requires` is untouched. 1. `VPYTHON_PURE_PYTHON=1` builds with no C extension, producing a `py3-none-any` wheel. micropip (and any other wasm installer) cannot install a platform wheel, and merely DECLARING `ext_modules` is what makes every wheel a platform wheel — so the key is now omitted entirely for that build rather than set to an empty list, which would not have changed the tag. Nothing is lost but speed: `_vector_import_helper` already falls back to the pure-Python `vector` when `cyvector` is unavailable. 2. `vpython/__init__.py` uses `importlib.metadata` instead of `pkg_resources`. pkg_resources is deprecated upstream and simply absent in Pyodide, so importing vpython there failed on the package's very first line. `python_requires` moves to >=3.8 accordingly (importlib.metadata is 3.8+; `notebook>=7` already required 3.8+, so this narrows nothing in practice). Verified in a real Pyodide 3.13.2 Web Worker, installing this branch's own pure wheel with `deps=False` and no setuptools present: OK vpython.vector OK vpython.vpython PACKAGE OK __version__ = 7.6.5 __gs_version__ = 3.2 `__gs_version__` resolving also confirms `gs_version.py` reads the bundled glow.min.js fine there, and that it is on the same 3.2 line trinket serves. Both builds were checked: with the flag, `vpython-7.6.5-py3-none-any.whl`; without it, `vpython-7.6.5-cp314-cp314-macosx_10_15_universal2.whl` as before. Execution now reaches the transport seam — `sphere()` stops at vpython.py:267 `from .no_notebook import _` (autobahn), which is the next piece of work, not a packaging problem.
sspickle · Aug 10, 2026 · Aug 10, 2026 · Aug 10, 2026 · Aug 10, 2026 · Aug 10, 2026
commit 3c0670431e3f33b9ba845001ab490dda71a8f0fb
diff --git a/setup.py b/setup.py
@@ -1,13 +1,28 @@
+import os
+
 from setuptools import setup
 
 from distutils.extension import Extension
 
-try:
-    from Cython.Build import cythonize
-    USE_CYTHON = True
-    extensions = cythonize('vpython/cyvector.pyx')
-except ImportError:
-    extensions = [Extension('vpython.cyvector', ['vpython/cyvector.c'])]
+# Set VPYTHON_PURE_PYTHON=1 to build with no C extension at all. The result is a
+# `py3-none-any` wheel, which is what Pyodide/micropip and other wasm targets
+# require — they cannot install a platform wheel, and declaring `ext_modules` is
+# what makes every wheel a platform wheel.
+#
+# Nothing is lost but speed: `_vector_import_helper` already falls back to the
+# pure-Python `vector` implementation when `cyvector` cannot be imported, so the
+# same source runs either way. Ordinary builds are unchanged — this is opt-in.
+PURE_PYTHON = os.environ.get('VPYTHON_PURE_PYTHON', '').strip() not in ('', '0', 'false', 'False')
+
+if PURE_PYTHON:
+    extensions = []
+else:
+    try:
+        from Cython.Build import cythonize
+        USE_CYTHON = True
+        extensions = cythonize('vpython/cyvector.pyx')
+    except ImportError:
+        extensions = [Extension('vpython.cyvector', ['vpython/cyvector.c'])]
 
 
 install_requires = ['jupyter', 'jupyter-server-proxy', 'jupyterlab-vpython>=3.1.8', 'notebook>=7.0.0', 'numpy', 'ipykernel',
@@ -35,14 +50,19 @@
           'Topic :: Multimedia :: Graphics :: 3D Rendering',
           'Topic :: Scientific/Engineering :: Visualization',
     ],
-    ext_modules=extensions,
     install_requires=install_requires,
-    python_requires=">=3.8",
+    python_requires=">=3.8",   # importlib.metadata, used in vpython/__init__.py
     package_data={'vpython': ['vpython_data/*',
                               'vpython_libraries/*',
                               'vpython_libraries/images/*']},
 )
 
+# `ext_modules` is added only for a normal build. Omitting the key entirely (as
+# opposed to passing an empty list) is what makes setuptools tag the wheel
+# `py3-none-any` rather than a platform wheel.
+if not PURE_PYTHON:
+    setup_args['ext_modules'] = extensions
+
 try:
     setup(**setup_args)
 except SystemExit as e:

diff --git a/vpython/__init__.py b/vpython/__init__.py
@@ -1,6 +1,7 @@
 # importlib.metadata, not pkg_resources: fresh Python 3.12+ environments no
 # longer ship setuptools, so `import pkg_resources` raises ModuleNotFoundError
-# the moment `import vpython` runs (caught by CI's macos-3.12 leg).
+# the moment `import vpython` runs (caught by CI's macos-3.12 leg). The same
+# import is simply absent on Pyodide/wasm, so this also unblocks wasm targets.
 from importlib.metadata import version as _dist_version, PackageNotFoundError
 
 from .gs_version import glowscript_version