Gate pybamm behind sys_platform marker for Pyodide compatibility

pyproject.toml

@@ -27,7 +27,11 @@ classifiers = [
 ]
 dependencies = [
     "pathsim>=0.22",
-    "pybamm>=25.12",
+    # PyBaMM ships native code that can't be installed in Pyodide. The
+    # marker resolves to a normal eager install on every real platform and
+    # is skipped on Emscripten so the pure-Python parts of the toolbox
+    # (`pathsim_batt.thermal`) still install in the browser.
+    "pybamm>=25.12; sys_platform != 'emscripten'",
 ]
 
 [project.optional-dependencies]

src/pathsim_batt/__init__.py

@@ -10,19 +10,26 @@
 except ImportError:
     __version__ = "unknown"
 
-from .cells import (
-    CellCoSimElectrical,
-    CellCoSimElectrothermal,
-    CellElectrical,
-    CellElectrothermal,
-)
 from .thermal import LumpedThermal
 
-__all__ = [
-    "__version__",
-    "CellElectrical",
-    "CellElectrothermal",
-    "CellCoSimElectrical",
-    "CellCoSimElectrothermal",
-    "LumpedThermal",
-]
+__all__ = ["__version__", "LumpedThermal"]
+
+# Cell blocks rely on pybamm (+ its casadi backend), which can't load in
+# Pyodide. Re-export them only when the import succeeds; on a normal pip
+# install both submodules load eagerly.
+try:
+    from .cells import (
+        CellCoSimElectrical,
+        CellCoSimElectrothermal,
+        CellElectrical,
+        CellElectrothermal,
+    )
+
+    __all__ += [
+        "CellElectrical",
+        "CellElectrothermal",
+        "CellCoSimElectrical",
+        "CellCoSimElectrothermal",
+    ]
+except ImportError:
+    pass