add missing module

Author: rabernat

src/zarr/strings.py

@@ -0,0 +1,36 @@
+from typing import Any
+from warnings import warn
+
+import numpy as np
+
+try:
+    STRING_DTYPE = np.dtype("T")
+    NUMPY_SUPPORTS_VLEN_STRING = True
+except TypeError:
+    STRING_DTYPE = np.dtype("object")
+    NUMPY_SUPPORTS_VLEN_STRING = False
+
+
+def cast_to_string_dtype(
+    data: np.ndarray[Any, np.dtype[Any]], safe: bool = False
+) -> np.ndarray[Any, np.dtype[Any]]:
+    if np.issubdtype(data.dtype, np.str_):
+        return data
+    if np.issubdtype(data.dtype, np.object_):
+        if NUMPY_SUPPORTS_VLEN_STRING:
+            try:
+                # cast to variable-length string dtype, fail if object contains non-string data
+                # mypy says "error: Unexpected keyword argument "coerce" for "StringDType"  [call-arg]"
+                return data.astype(np.dtypes.StringDType(coerce=False), copy=False)  # type: ignore[call-arg]
+            except ValueError as e:
+                raise ValueError("Cannot cast object dtype to string dtype") from e
+        else:
+            out = data.astype(np.str_)
+            if not safe:
+                warn(
+                    f"Casted object dtype to string dtype {out.dtype}. To avoid this warning, "
+                    "cast the data to a string dtype before passing to Zarr or upgrade to NumPy >= 2.",
+                    stacklevel=2,
+                )
+            return out
+    raise ValueError(f"Cannot cast dtype {data.dtype} to string dtype")