clean up docstring

src/pymatgen/core/composition.py

@@ -25,7 +25,7 @@
 
 if TYPE_CHECKING:
     from collections.abc import Generator, Iterator
-    from typing import Any, ClassVar
+    from typing import Any, ClassVar, Literal
 
     from typing_extensions import Self
 
@@ -774,17 +774,25 @@ def to_reduced_dict(self) -> dict[str, float]:
     def to_weight_dict(self) -> dict[str, float]:
         """
         Returns:
-            dict[str, float] with weight fraction of each component {"Ti": 0.90, "V": 0.06, "Al": 0.04}.
+            dict[str, float]: weight fractions of each component, e.g. {"Ti": 0.90, "V": 0.06, "Al": 0.04}.
         """
         return {str(el): self.get_wt_fraction(el) for el in self.elements}
 
     @property
-    def to_data_dict(self) -> dict[str, Any]:
+    def to_data_dict(
+        self,
+    ) -> dict[
+        Literal["reduced_cell_composition", "unit_cell_composition", "reduced_cell_formula", "elements", "nelements"],
+        Any,
+    ]:
         """
         Returns:
-            A dict with many keys and values relating to Composition/Formula,
-            including reduced_cell_composition, unit_cell_composition,
-            reduced_cell_formula, elements and nelements.
+            dict with the following keys:
+                - reduced_cell_composition
+                - unit_cell_composition
+                - reduced_cell_formula
+                - elements
+                - nelements.
         """
         return {
             "reduced_cell_composition": self.reduced_composition,
@@ -802,7 +810,7 @@ def charge(self) -> float | None:
         """
         warnings.warn(
             "Composition.charge is experimental and may produce incorrect results. Use with "
-            "caution and open a GitHub issue pinging @janosh to report bad behavior."
+            "caution and open a GitHub issue pinging @janosh to report bad behavior.",
         )
         oxi_states = [getattr(specie, "oxi_state", None) for specie in self]
         if {*oxi_states} <= {0, None}:
@@ -818,7 +826,7 @@ def charge_balanced(self) -> bool | None:
         """
         warnings.warn(
             "Composition.charge_balanced is experimental and may produce incorrect results. "
-            "Use with caution and open a GitHub issue pinging @janosh to report bad behavior."
+            "Use with caution and open a GitHub issue pinging @janosh to report bad behavior.",
         )
         if self.charge is None:
             if {getattr(el, "oxi_state", None) for el in self} == {0}:
@@ -917,7 +925,7 @@ def replace(self, elem_map: dict[str, str | dict[str, float]]) -> Self:
                 if el in self:
                     warnings.warn(
                         f"Same element ({el}) in both the keys and values of the substitution!"
-                        "This can be ambiguous, so be sure to check your result."
+                        "This can be ambiguous, so be sure to check your result.",
                     )
 
         return type(self)(new_comp)