gh-127740: For odd-length input to bytes.fromhex(...) change the error message to ValueError: fromhex() arg must be of even length

Author: srinivasreddy

Lib/test/test_bytes.py

@@ -459,6 +459,11 @@ def test_fromhex(self):
         self.assertRaises(ValueError, self.type2test.fromhex, '\x00')
         self.assertRaises(ValueError, self.type2test.fromhex, '12   \x00   34')
 
+        # For odd number of character(s)
+        with self.assertRaises(ValueError) as cm:
+            self.type2test.fromhex("a")
+        self.assertIn("fromhex() arg must be of even length", str(cm.exception))
+
         for data, pos in (
             # invalid first hexadecimal character
             ('12 x4 56', 3),

Objects/bytesobject.c

@@ -2490,7 +2490,7 @@ PyObject*
 _PyBytes_FromHex(PyObject *string, int use_bytearray)
 {
     char *buf;
-    Py_ssize_t hexlen, invalid_char;
+    Py_ssize_t hexlen, invalid_char,real_len=0;
     unsigned int top, bot;
     const Py_UCS1 *str, *end;
     _PyBytesWriter writer;
@@ -2516,6 +2516,19 @@ _PyBytes_FromHex(PyObject *string, int use_bytearray)
     }
 
     assert(PyUnicode_KIND(string) == PyUnicode_1BYTE_KIND);
+
+    const Py_UCS1 *s = PyUnicode_1BYTE_DATA(string);
+    for (Py_ssize_t i = 0; i < hexlen; i++) {
+        if (!Py_ISSPACE(s[i])) {
+            real_len++;
+        }
+    }
+    if (real_len % 2 != 0) {
+        PyErr_SetString(PyExc_ValueError,
+                       "fromhex() arg must be of even length");
+        _PyBytesWriter_Dealloc(&writer);
+        return NULL;
+    }
     str = PyUnicode_1BYTE_DATA(string);
 
     /* This overestimates if there are spaces */