Make is_nonstringy_sequence available in types. (#126)

Gives `is_normal_sequence` a slightly better name and makes it available
to packages importing somacore.

python-spec/src/somacore/query/axis.py

@@ -1,11 +1,11 @@
-from typing import Any, Optional, Sequence, Tuple
+from typing import Optional, Sequence, Tuple
 
 import attrs
 import numpy as np
 import pyarrow as pa
-from typing_extensions import TypeGuard
 
 from .. import options
+from .. import types
 
 
 def _canonicalize_coords(
@@ -22,7 +22,7 @@ def _canonicalize_coords(
         raise TypeError(
             f"query coordinates must be a sequence, not a single {type(in_coords)}"
         )
-    if not _is_normal_sequence(in_coords):
+    if not types.is_nonstringy_sequence(in_coords):
         raise TypeError(
             "query coordinates must be a normal sequence, not `str` or `bytes`."
         )
@@ -42,10 +42,6 @@ def _canonicalize_coord(coord: options.SparseDFCoord) -> options.SparseDFCoord:
     raise TypeError(f"{type(coord)} object cannot be used as a coordinate.")
 
 
-def _is_normal_sequence(it: Any) -> TypeGuard[Sequence]:
-    return not isinstance(it, (str, bytes)) and isinstance(it, Sequence)
-
-
 @attrs.define(frozen=True, kw_only=True)
 class AxisQuery:
     """Single-axis dataframe query with coordinates and a value filter.

python-spec/src/somacore/types.py

@@ -1,7 +1,17 @@
 """Type and interface declarations that are not specific to options."""
 
-from typing import Optional, TypeVar
-from typing_extensions import Protocol, Self, runtime_checkable
+from typing import Any, Optional, TypeVar, Sequence
+from typing_extensions import Protocol, Self, runtime_checkable, TypeGuard
+
+
+def is_nonstringy_sequence(it: Any) -> TypeGuard[Sequence]:
+    """Returns true if a sequence is a "normal" sequence and not str or bytes.
+
+    str and bytes are "weird" sequences because iterating them gives you
+    another str or bytes instance for each character, and when used as a
+    sequence is not what users want.
+    """
+    return not isinstance(it, (str, bytes)) and isinstance(it, Sequence)
 
 
 class Comparable(Protocol):

python-spec/testing/test_types.py

@@ -0,0 +1,21 @@
+from typing import Any, Iterable
+import unittest
+
+from somacore import types
+
+
+class TestTypes(unittest.TestCase):
+    def test_is_nonstringy_sequence(self):
+        seqs: Iterable[Any] = ([], (), range(10))
+        for seq in seqs:
+            with self.subTest(seq):
+                self.assertTrue(types.is_nonstringy_sequence(seq))
+
+        non_seqs: Iterable[Any] = (1, "hello", b"goodbye", (x for x in range(10)))
+        for non_seq in non_seqs:
+            with self.subTest(non_seq):
+                self.assertFalse(types.is_nonstringy_sequence(non_seq))
+
+    def test_slice(self):
+        self.assertIsInstance(slice(None), types.Slice)
+        self.assertNotIsInstance((1, 2), types.Slice)