DM-38492: Move ResourcePathExpression definition to end of file

doc/changes/DM-38492.misc.rst

@@ -0,0 +1 @@
+* ``ResourcePathExpression`` can now be used in an `isinstance()` call on Python 3.10 and newer.

python/lsst/resources/_resourcePath.py

@@ -63,11 +63,6 @@
 MAX_WORKERS = 10
 
 
-ResourcePathExpression = Union[str, urllib.parse.ParseResult, "ResourcePath", Path]
-"""Type-annotation alias for objects that can be coerced to ResourcePath.
-"""
-
-
 class ResourcePath:
     """Convenience wrapper around URI parsers.
 
@@ -1404,3 +1399,8 @@ def _openImpl(
             out_bytes = str_buffer.getvalue().encode(encoding)
         if "r" not in mode or "+" in mode:
             self.write(out_bytes, overwrite=("x" not in mode))
+
+
+ResourcePathExpression = Union[str, urllib.parse.ParseResult, ResourcePath, Path]
+"""Type-annotation alias for objects that can be coerced to ResourcePath.
+"""

tests/test_file.py

@@ -11,14 +11,35 @@
 
 import os
 import pathlib
+import sys
 import unittest
 import unittest.mock
+import urllib.parse
 
-from lsst.resources import ResourcePath
+from lsst.resources import ResourcePath, ResourcePathExpression
 from lsst.resources.tests import GenericReadWriteTestCase, GenericTestCase
 
 TESTDIR = os.path.abspath(os.path.dirname(__file__))
 
+_OLD_PYTHON = False
+if sys.version_info < (3, 10, 0):
+    _OLD_PYTHON = True
+
+
+class SimpleTestCase(unittest.TestCase):
+    @unittest.skipIf(_OLD_PYTHON, "isinstance() with unions is not supported.")
+    def test_instance(self):
+        for example in (
+            "xxx",
+            ResourcePath("xxx"),
+            pathlib.Path("xxx"),
+            urllib.parse.urlparse("file:///xxx"),
+        ):
+            self.assertIsInstance(example, ResourcePathExpression)
+
+        for example in ({1, 2, 3}, 42, self):
+            self.assertNotIsInstance(example, ResourcePathExpression)
+
 
 class FileTestCase(GenericTestCase, unittest.TestCase):
     scheme = "file"