Speed up the generation of no-member suggestions

pylint/checkers/typecheck.py

@@ -150,8 +150,12 @@ def _(node: nodes.ClassDef | bases.Instance) -> Iterable[str]:
     return itertools.chain(values, other_values)
 
 
-def _string_distance(seq1: str, seq2: str) -> int:
-    seq2_length = len(seq2)
+def _string_distance(seq1: str, seq2: str, seq1_length: int, seq2_length: int) -> int:
+    if not seq1_length:
+        return seq2_length
+
+    if not seq2_length:
+        return seq1_length
 
     row = [*list(range(1, seq2_length + 1)), 0]
     for seq1_index, seq1_char in enumerate(seq1):
@@ -182,11 +186,20 @@ def _similar_names(
     possible_names: list[tuple[str, int]] = []
     names = _node_names(owner)
 
+    attr_str = attrname or ""
+    attr_len = len(attr_str)
+
     for name in names:
         if name == attrname:
             continue
 
-        distance = _string_distance(attrname or "", name)
+        name_len = len(name)
+
+        min_distance = abs(attr_len - name_len)
+        if min_distance > distance_threshold:
+            continue
+
+        distance = _string_distance(attr_str, name, attr_len, name_len)
         if distance <= distance_threshold:
             possible_names.append((name, distance))
 

tests/checkers/unittest_typecheck.py

@@ -221,3 +221,47 @@ def decorated():
             )
         ):
             self.checker.visit_subscript(subscript)
+
+
+class TestTypeCheckerStringDistance:
+    """Tests for the _string_distance helper in pylint.checkers.typecheck."""
+
+    def test_string_distance_identical_strings(self) -> None:
+        seq1 = "hi"
+        seq2 = "hi"
+        assert typecheck._string_distance(seq1, seq2, len(seq1), len(seq2)) == 0
+
+        seq1, seq2 = seq2, seq1
+        assert typecheck._string_distance(seq1, seq2, len(seq1), len(seq2)) == 0
+
+    def test_string_distance_empty_string(self) -> None:
+        seq1 = ""
+        seq2 = "hi"
+        assert typecheck._string_distance(seq1, seq2, len(seq1), len(seq2)) == 2
+
+        seq1, seq2 = seq2, seq1
+        assert typecheck._string_distance(seq1, seq2, len(seq1), len(seq2)) == 2
+
+    def test_string_distance_edit_distance_one_character(self) -> None:
+        seq1 = "hi"
+        seq2 = "he"
+        assert typecheck._string_distance(seq1, seq2, len(seq1), len(seq2)) == 1
+
+        seq1, seq2 = seq2, seq1
+        assert typecheck._string_distance(seq1, seq2, len(seq1), len(seq2)) == 1
+
+    def test_string_distance_edit_distance_multiple_similar_characters(self) -> None:
+        seq1 = "hello"
+        seq2 = "yelps"
+        assert typecheck._string_distance(seq1, seq2, len(seq1), len(seq2)) == 3
+
+        seq1, seq2 = seq2, seq1
+        assert typecheck._string_distance(seq1, seq2, len(seq1), len(seq2)) == 3
+
+    def test_string_distance_edit_distance_all_dissimilar_characters(self) -> None:
+        seq1 = "yellow"
+        seq2 = "orange"
+        assert typecheck._string_distance(seq1, seq2, len(seq1), len(seq2)) == 6
+
+        seq1, seq2 = seq2, seq1
+        assert typecheck._string_distance(seq1, seq2, len(seq1), len(seq2)) == 6