Fix ValueError: Invalid fmt with Structure.to(fmt='yml') (#3557)

* fix Structure.to(fmt='yml'), add Structure.FileFormats to ensure consistent format support and value err msg in Structure.to and Structure.from_file

* test_structure.py cover fmt='yml' in test_to_from_file_string

fix pytest.raises expected msg

pymatgen/core/structure.py

@@ -60,6 +60,8 @@
 
     from pymatgen.util.typing import CompositionLike, SpeciesLike
 
+FileFormats = Literal["cif", "poscar", "cssr", "json", "yaml", "yml", "xsf", "mcsqs", "res", ""]
+
 
 class Neighbor(Site):
     """Simple Site subclass to contain a neighboring atom that skips all the unnecessary checks for speed. Can be
@@ -447,13 +449,13 @@ def is_valid(self, tol: float = DISTANCE_TOLERANCE) -> bool:
         return np.min(all_dists) > tol
 
     @abstractmethod
-    def to(self, filename: str = "", fmt: str = "") -> str | None:
+    def to(self, filename: str = "", fmt: FileFormats = "") -> str | None:
         """Generates string representations (cif, json, poscar, ....) of SiteCollections (e.g.,
         molecules / structures). Should return str or None if written to a file.
         """
         raise NotImplementedError
 
-    def to_file(self, filename: str = "", fmt: str = "") -> str | None:
+    def to_file(self, filename: str = "", fmt: FileFormats = "") -> str | None:
         """A more intuitive alias for .to()."""
         return self.to(filename, fmt)
 
@@ -2653,7 +2655,7 @@ def from_dict(cls, dct: dict[str, Any], fmt: Literal["abivars"] | None = None) -
         charge = dct.get("charge")
         return cls.from_sites(sites, charge=charge, properties=dct.get("properties"))
 
-    def to(self, filename: str | Path = "", fmt: str = "", **kwargs) -> str:
+    def to(self, filename: str | Path = "", fmt: FileFormats = "", **kwargs) -> str:
         """Outputs the structure to a file or string.
 
         Args:
@@ -2663,7 +2665,7 @@ def to(self, filename: str | Path = "", fmt: str = "", **kwargs) -> str:
             fmt (str): Format to output to. Defaults to JSON unless filename
                 is provided. If fmt is specifies, it overrides whatever the
                 filename is. Options include "cif", "poscar", "cssr", "json",
-                "xsf", "mcsqs", "prismatic", "yaml", "fleur-inpgen".
+                "xsf", "mcsqs", "prismatic", "yaml", "yml", "fleur-inpgen".
                 Non-case sensitive.
             **kwargs: Kwargs passthru to relevant methods. E.g., This allows
                 the passing of parameters like symprec to the
@@ -2673,7 +2675,7 @@ def to(self, filename: str | Path = "", fmt: str = "", **kwargs) -> str:
             str: String representation of molecule in given format. If a filename
                 is provided, the same string is written to the file.
         """
-        filename, fmt = str(filename), fmt.lower()
+        filename, fmt = str(filename), cast(FileFormats, fmt.lower())
 
         if fmt == "cif" or fnmatch(filename.lower(), "*.cif*"):
             from pymatgen.io.cif import CifWriter
@@ -2722,7 +2724,7 @@ def to(self, filename: str | Path = "", fmt: str = "", **kwargs) -> str:
             from pymatgen.io.prismatic import Prismatic
 
             return Prismatic(self).to_str()
-        elif fmt == "yaml" or fnmatch(filename, "*.yaml*") or fnmatch(filename, "*.yml*"):
+        elif fmt in ("yaml", "yml") or fnmatch(filename, "*.yaml*") or fnmatch(filename, "*.yml*"):
             yaml = YAML()
             str_io = StringIO()
             yaml.dump(self.as_dict(), str_io)
@@ -2747,7 +2749,7 @@ def to(self, filename: str | Path = "", fmt: str = "", **kwargs) -> str:
         else:
             if fmt == "":
                 raise ValueError(f"Format not specified and could not infer from {filename=}")
-            raise ValueError(f"Invalid format={fmt!r}")
+            raise ValueError(f"Invalid {fmt=}, valid options are {get_args(FileFormats)}")
 
         if filename:
             writer.write_file(filename)
@@ -2757,7 +2759,7 @@ def to(self, filename: str | Path = "", fmt: str = "", **kwargs) -> str:
     def from_str(  # type: ignore[override]
         cls,
         input_string: str,
-        fmt: Literal["cif", "poscar", "cssr", "json", "yaml", "xsf", "mcsqs", "res"],
+        fmt: FileFormats,
         primitive: bool = False,
         sort: bool = False,
         merge_tol: float = 0.0,
@@ -2768,7 +2770,7 @@ def from_str(  # type: ignore[override]
         Args:
             input_string (str): String to parse.
             fmt (str): A file format specification. One of "cif", "poscar", "cssr",
-                "json", "yaml", "xsf", "mcsqs".
+                "json", "yaml", "yml", "xsf", "mcsqs", "res".
             primitive (bool): Whether to find a primitive cell. Defaults to
                 False.
             sort (bool): Whether to sort the sites in accordance to the default
@@ -2797,12 +2799,12 @@ def from_str(  # type: ignore[override]
             cssr = Cssr.from_str(input_string, **kwargs)
             struct = cssr.structure
         elif fmt_low == "json":
-            d = json.loads(input_string)
-            struct = Structure.from_dict(d)
-        elif fmt_low == "yaml":
+            dct = json.loads(input_string)
+            struct = Structure.from_dict(dct)
+        elif fmt_low in ("yaml", "yml"):
             yaml = YAML()
-            d = yaml.load(input_string)
-            struct = Structure.from_dict(d)
+            dct = yaml.load(input_string)
+            struct = Structure.from_dict(dct)
         elif fmt_low == "xsf":
             from pymatgen.io.xcrysden import XSF
 
@@ -2825,7 +2827,7 @@ def from_str(  # type: ignore[override]
 
             struct = ResIO.structure_from_str(input_string, **kwargs)
         else:
-            raise ValueError(f"Unrecognized format `{fmt}`!")
+            raise ValueError(f"Invalid {fmt=}, valid options are {get_args(FileFormats)}")
 
         if sort:
             struct = struct.get_sorted_structure()

tests/core/test_structure.py

@@ -818,7 +818,7 @@ def test_get_dist_matrix(self):
         assert_allclose(self.struct.distance_matrix, ans)
 
     def test_to_from_file_and_string(self):
-        for fmt in ["cif", "json", "poscar", "cssr"]:
+        for fmt in ("cif", "json", "poscar", "cssr"):
             struct = self.struct.to(fmt=fmt)
             assert struct is not None
             ss = IStructure.from_str(struct, fmt=fmt)
@@ -851,7 +851,7 @@ def test_to_from_file_and_string(self):
 
         with pytest.raises(ValueError, match="Format not specified and could not infer from filename='whatever'"):
             self.struct.to(filename="whatever")
-        with pytest.raises(ValueError, match="Invalid format='badformat'"):
+        with pytest.raises(ValueError, match="Invalid fmt='badformat'"):
             self.struct.to(fmt="badformat")
 
         self.struct.to(filename=(gz_json_path := "POSCAR.testing.gz"))
@@ -1284,7 +1284,7 @@ def test_to_from_abivars(self):
 
     def test_to_from_file_string(self):
         # to/from string
-        for fmt in ["cif", "json", "poscar", "cssr", "yaml", "xsf", "res"]:
+        for fmt in ("cif", "json", "poscar", "cssr", "yaml", "yml", "xsf", "res"):
             struct = self.struct.to(fmt=fmt)
             assert struct is not None
             ss = Structure.from_str(struct, fmt=fmt)