Add env var expansion to schemeless ButlerURI

python/lsst/daf/butler/core/_butlerUri/schemeless.py

@@ -129,7 +129,8 @@ def _fixupPathUri(parsed: urllib.parse.ParseResult, root: Optional[Union[str, Bu
         to be turned into absolute paths before they can be used.  This is
         always done regardless of the ``forceAbsolute`` parameter.
 
-        Scheme-less paths are normalized.
+        Scheme-less paths are normalized and environment variables are
+        expanded.
         """
         # assume we are not dealing with a directory URI
         dirLike = False
@@ -148,6 +149,10 @@ def _fixupPathUri(parsed: urllib.parse.ParseResult, root: Optional[Union[str, Bu
         # we quoted it in the constructor so unquote here
         expandedPath = os.path.expanduser(urllib.parse.unquote(parsed.path))
 
+        # We might also be receiving a path containing environment variables
+        # so expand those here
+        expandedPath = os.path.expandvars(expandedPath)
+
         # Ensure that this becomes a file URI if it is already absolute
         if os.path.isabs(expandedPath):
             replacements["scheme"] = "file"

tests/test_uri.py

@@ -101,6 +101,19 @@ def testRelative(self):
         child = ButlerURI("../c/e/f/g.txt", forceAbsolute=False)
         self.assertEqual(child.relative_to(parent), "e/f/g.txt")
 
+    def testEnvVar(self):
+        """Test that environment variables are expanded."""
+
+        with unittest.mock.patch.dict(os.environ, {"MY_TEST_DIR": "/a/b/c"}):
+            uri = ButlerURI("${MY_TEST_DIR}/d.txt")
+        self.assertEqual(uri.path, "/a/b/c/d.txt")
+        self.assertEqual(uri.scheme, "file")
+
+        # This will not expand
+        uri = ButlerURI("${MY_TEST_DIR}/d.txt", forceAbsolute=False)
+        self.assertEqual(uri.path, "${MY_TEST_DIR}/d.txt")
+        self.assertFalse(uri.scheme)
+
     def testMkdir(self):
         tmpdir = ButlerURI(self.tmpdir)
         newdir = tmpdir.join("newdir/seconddir")