From 6ca3d6fb3d1a6f5466f4dfbc819e0ffd8c27d040 Mon Sep 17 00:00:00 2001
From: KevinRK29 <kevinrk2000@gmail.com>
Date: Fri, 30 Jan 2026 01:06:15 -0500
Subject: [PATCH 1/3] added fuzzy matching for name not defined errors

---
 mypy/semanal.py | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/mypy/semanal.py b/mypy/semanal.py
index 20bcb2f4ac60a..e6bd2d835f69f 100644
--- a/mypy/semanal.py
+++ b/mypy/semanal.py
@@ -7475,6 +7475,12 @@ def name_not_defined(self, name: str, ctx: Context, namespace: str | None = None
             self.record_incomplete_ref()
             return
         message = f'Name "{name}" is not defined'
+        # Collect all names in scope to suggest similar alternatives
+        alternatives = self._get_names_in_scope()
+        alternatives.discard(name)
+        matches = best_matches(name, alternatives, n=3)
+        if matches:
+            message += f"; did you mean {pretty_seq(matches, 'or')}?"
         self.fail(message, ctx, code=codes.NAME_DEFINED)
 
         if f"builtins.{name}" in SUGGESTED_TEST_FIXTURES:
@@ -7499,6 +7505,36 @@ def name_not_defined(self, name: str, ctx: Context, namespace: str | None = None
             ).format(module=module, name=lowercased[fullname].rsplit(".", 1)[-1])
             self.note(hint, ctx, code=codes.NAME_DEFINED)
 
+    def _get_names_in_scope(self) -> set[str]:
+        """Collect all names visible in the current scope for fuzzy matching suggestions.
+
+        This includes:
+        - Local variables (from function scopes)
+        - Class attributes (if it's inside a class)
+        - Global/module-level names
+        - Builtins
+        """
+        names: set[str] = set()
+
+        for table in self.locals:
+            if table is not None:
+                names.update(table.keys())
+
+        if self.type is not None:
+            names.update(self.type.names.keys())
+
+        names.update(self.globals.keys())
+
+        b = self.globals.get("__builtins__", None)
+        if b and isinstance(b.node, MypyFile):
+            # Only include public builtins (not _private ones)
+            for builtin_name in b.node.names.keys():
+                if not (len(builtin_name) > 1 and builtin_name[0] == "_" and builtin_name[1] != "_"):
+                    names.add(builtin_name)
+
+        # Filter out internal/dunder names that aren't useful for suggestions and might introduce noise
+        return {n for n in names if not n.startswith("__") or n.endswith("__")}
+
     def already_defined(
         self, name: str, ctx: Context, original_ctx: SymbolTableNode | SymbolNode | None, noun: str
     ) -> None:

From 115b8316b86e30afbf66c5f7d7700393f076caa9 Mon Sep 17 00:00:00 2001
From: KevinRK29 <kevinrk2000@gmail.com>
Date: Fri, 30 Jan 2026 01:06:20 -0500
Subject: [PATCH 2/3] added test to validate suggestions

---
 test-data/unit/check-errorcodes.test | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/test-data/unit/check-errorcodes.test b/test-data/unit/check-errorcodes.test
index 58f48144b3e56..eca5a2e687c80 100644
--- a/test-data/unit/check-errorcodes.test
+++ b/test-data/unit/check-errorcodes.test
@@ -21,6 +21,25 @@ def f() -> None:
 [file m.py]
 [builtins fixtures/module.pyi]
 
+[case testErrorCodeUndefinedNameSuggestion]
+my_variable = 42
+my_constant = 100
+
+x = my_variabel  # E: Name "my_variabel" is not defined; did you mean "my_variable"?  [name-defined]
+
+def calculate_sum(items: int) -> int:
+    return items
+
+calculate_summ(1)  # E: Name "calculate_summ" is not defined; did you mean "calculate_sum"?  [name-defined]
+
+class MyClass:
+    pass
+
+y = MyClas()  # E: Name "MyClas" is not defined; did you mean "MyClass"?  [name-defined]
+
+unknown_xyz  # E: Name "unknown_xyz" is not defined  [name-defined]
+[builtins fixtures/module.pyi]
+
 [case testErrorCodeUnclassifiedError]
 class A:
     def __init__(self) -> int: \

From ac380215449d999aeb2b677029f4c69070b2532a Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Fri, 30 Jan 2026 06:13:41 +0000
Subject: [PATCH 3/3] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 mypy/semanal.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mypy/semanal.py b/mypy/semanal.py
index e6bd2d835f69f..0c4647eaf625c 100644
--- a/mypy/semanal.py
+++ b/mypy/semanal.py
@@ -7529,7 +7529,9 @@ def _get_names_in_scope(self) -> set[str]:
         if b and isinstance(b.node, MypyFile):
             # Only include public builtins (not _private ones)
             for builtin_name in b.node.names.keys():
-                if not (len(builtin_name) > 1 and builtin_name[0] == "_" and builtin_name[1] != "_"):
+                if not (
+                    len(builtin_name) > 1 and builtin_name[0] == "_" and builtin_name[1] != "_"
+                ):
                     names.add(builtin_name)
 
         # Filter out internal/dunder names that aren't useful for suggestions and might introduce noise