Reset label for sites changed by Structure.replace_species()

pymatgen/core/sites.py

@@ -101,7 +101,7 @@ def label(self) -> str:
         return self._label if self._label is not None else self.species_string
 
     @label.setter
-    def label(self, label: str) -> None:
+    def label(self, label: str | None) -> None:
         self._label = label
 
     @property

pymatgen/core/structure.py

@@ -528,11 +528,13 @@ def replace_species(
     ) -> SiteCollection:
         """Swap species.
 
+        Note that this clears the label of any affected site.
+
         Args:
             species_mapping (dict): Species to swap. Species can be elements too. E.g.,
                 {Element("Li"): Element("Na")} performs a Li for Na substitution. The second species can
                 be a sp_and_occu dict. For example, a site with 0.5 Si that is passed the mapping
-                {Element('Si): {Element('Ge'): 0.75, Element('C'): 0.25} } will have .375 Ge and .125 C.
+                {Element('Si'): {Element('Ge'): 0.75, Element('C'): 0.25} } will have .375 Ge and .125 C.
             in_place (bool): Whether to perform the substitution in place or modify a copy.
                 Defaults to True.
 
@@ -559,6 +561,7 @@ def replace_species(
                     except Exception:
                         comp += {new_sp: amt}
                 site.species = comp
+                site.label = None  # type: ignore
 
         return site_coll
 

tests/core/test_structure.py

@@ -977,6 +977,12 @@ def test_replace_species(self):
         assert struct.formula == "K1.5 P0.5"
         assert new_struct.formula == "Li1.5 P0.5"
 
+    def test_replace_species_labels(self):
+        """https://github.com/materialsproject/pymatgen/issues/3658"""
+        struct = self.labeled_structure
+        struct.replace_species({"Si": "Ge"})
+        assert struct.labels == ["Ge", "Ge"]
+
     def test_append_insert_remove_replace_substitute(self):
         struct = self.struct
         struct.insert(1, "O", [0.5, 0.5, 0.5])