Better approach suggested by @sigmavirus24

This required adding a test to cover the line where the validator
has already been created.

Author: handrews

src/rfc3986/_mixin.py

@@ -56,14 +56,15 @@ def authority_info(self):
     def _match_subauthority(self):
         return misc.SUBAUTHORITY_MATCHER.match(self.authority)
 
-    def _get_base_uri_validator(self):
-        try:
-            return self._base_uri_validator
-        except AttributeError:
-            self._base_uri_validator = (
-                validators.Validator().require_presence_of("scheme")
-            )
-            return self._base_uri_validator
+    @property
+    def _validator(self):
+        v = getattr(self, "_cached_validator", None)
+        if v is not None:
+            return v
+        self._cached_validator = validators.Validator().require_presence_of(
+            "scheme"
+        )
+        return self._cached_validator
 
     @property
     def host(self):
@@ -272,7 +273,7 @@ def resolve_with(self, base_uri, strict=False):
             base_uri = type(self).from_string(base_uri)
 
         try:
-            self._get_base_uri_validator().validate(base_uri)
+            self._validator.validate(base_uri)
         except exc.ValidationError:
             raise exc.ResolutionError(base_uri)
 

tests/test_uri.py

@@ -363,6 +363,14 @@ def test_resolve_pathless_query(self, basic_uri):
         assert T.path is None
         assert T.query == "query"
 
+    def test_resolve_twice_for_cached_validator(self, basic_uri):
+        R = URIReference.from_string("")
+        B = URIReference.from_string(basic_uri)
+        T1 = R.resolve_with(B)
+        T2 = R.resolve_with(B)
+        assert T1 == T2
+        assert T1 == B
+
 
 def test_empty_querystrings_persist():
     url = "https://httpbin.org/get?"