From 9bc62536abed09d01443ed8024b52e17bdfb4eac Mon Sep 17 00:00:00 2001
From: Huanyi Xie <74809554+xiehuanyi@users.noreply.github.com>
Date: Thu, 8 Oct 2026 14:25:47 +0300
Subject: [PATCH] Require numeric check digits in CUSIP and SEDOL identifiers

---
 src/validators/finance.py |  4 ++--
 tests/test_finance.py     | 27 +++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/src/validators/finance.py b/src/validators/finance.py
index 9df5a970..38c76d70 100644
--- a/src/validators/finance.py
+++ b/src/validators/finance.py
@@ -71,7 +71,7 @@ def cusip(value: str):
         (Literal[True]): If `value` is a valid CUSIP string.
         (ValidationError): If `value` is an invalid CUSIP string.
     """
-    return len(value) == 9 and _cusip_checksum(value)
+    return len(value) == 9 and value[-1] in "0123456789" and _cusip_checksum(value)
 
 
 @validator
@@ -117,7 +117,7 @@ def sedol(value: str):
         (Literal[True]): If `value` is a valid SEDOL string.
         (ValidationError): If `value` is an invalid SEDOL string.
     """
-    if len(value) != 7:
+    if len(value) != 7 or value[-1] not in "0123456789":
         return False
 
     weights = [1, 3, 1, 7, 3, 9, 1]
diff --git a/tests/test_finance.py b/tests/test_finance.py
index a40fd333..ce221a73 100644
--- a/tests/test_finance.py
+++ b/tests/test_finance.py
@@ -1,5 +1,8 @@
 """Test Finance."""
 
+# standard
+from typing import Callable
+
 # external
 import pytest
 
@@ -49,3 +52,27 @@ def test_returns_true_on_valid_sedol(value: str):
 def test_returns_failed_validation_on_invalid_sedol(value: str):
     """Test returns failed validation on invalid sedol."""
     assert isinstance(sedol(value), ValidationError)
+
+
+@pytest.mark.parametrize(
+    "validate, value",
+    [
+        (cusip, "03783310J"),
+        (cusip, "03783310j"),
+        (cusip, "03783310@"),
+        (sedol, "293692L"),
+        (sedol, "B12345G"),
+        (sedol, "B12345Q"),
+    ],
+)
+def test_rejects_non_numeric_check_digit(validate: Callable[[str], object], value: str):
+    """Reject letters and symbols that accidentally satisfy the checksum."""
+    assert isinstance(validate(value), ValidationError)
+
+
+@pytest.mark.parametrize(
+    "validate, value", [(cusip, "037833100"), (sedol, "2936921"), (sedol, "B123456")]
+)
+def test_accepts_numeric_check_digit(validate: Callable[[str], object], value: str):
+    """Keep valid numeric check digits, including alphanumeric identifiers."""
+    assert validate(value) is True