Typing

src/pymatgen/core/composition.py

@@ -173,7 +173,7 @@ def __init__(self, *args, strict: bool = False, **kwargs) -> None:
         else:
             elem_map = dict(*args, **kwargs)  # type: ignore[assignment]
         elem_amt = {}
-        self._n_atoms = 0
+        self._n_atoms: int | float = 0
         for key, val in elem_map.items():
             if val < -type(self).amount_tolerance and not self.allow_negative:
                 raise ValueError("Amounts in Composition cannot be negative!")
@@ -184,7 +184,7 @@ def __init__(self, *args, strict: bool = False, **kwargs) -> None:
         if strict and not self.valid:
             raise ValueError(f"Composition is not valid, contains: {', '.join(map(str, self.elements))}")
 
-    def __getitem__(self, key: SpeciesLike) -> float:
+    def __getitem__(self, key: SpeciesLike) -> int | float:
         try:
             sp = get_el_sp(key)
             if isinstance(sp, Species):
@@ -202,7 +202,7 @@ def __len__(self) -> int:
     def __iter__(self) -> Iterator[Species | Element | DummySpecies]:
         return iter(self._data)
 
-    def items(self) -> ItemsView[Species | Element | DummySpecies, float]:
+    def items(self) -> ItemsView[Species | Element | DummySpecies, int | float]:
         """Returns Dict.items() for the Composition dict."""
         return self._data.items()