Issue #18829: csv.Dialect() now checks type for delimiter, escapechar and

quotechar fields.  Original patch by Vajrasky Kok.

Lib/test/test_csv.py

@@ -756,6 +756,7 @@ class mydialect(csv.Dialect):
             lineterminator = '\r\n'
             quoting = csv.QUOTE_NONE
         d = mydialect()
+        self.assertEqual(d.quoting, csv.QUOTE_NONE)
 
         mydialect.quoting = None
         self.assertRaises(csv.Error, mydialect)
@@ -764,12 +765,21 @@ class mydialect(csv.Dialect):
         mydialect.quoting = csv.QUOTE_ALL
         mydialect.quotechar = '"'
         d = mydialect()
+        self.assertEqual(d.quoting, csv.QUOTE_ALL)
+        self.assertEqual(d.quotechar, '"')
+        self.assertTrue(d.doublequote)
 
         mydialect.quotechar = "''"
-        self.assertRaises(csv.Error, mydialect)
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"quotechar" must be an 1-character string')
 
         mydialect.quotechar = 4
-        self.assertRaises(csv.Error, mydialect)
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"quotechar" must be string, not int')
 
     def test_delimiter(self):
         class mydialect(csv.Dialect):
@@ -780,12 +790,31 @@ class mydialect(csv.Dialect):
             lineterminator = '\r\n'
             quoting = csv.QUOTE_NONE
         d = mydialect()
+        self.assertEqual(d.delimiter, ";")
 
         mydialect.delimiter = ":::"
-        self.assertRaises(csv.Error, mydialect)
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"delimiter" must be an 1-character string')
+
+        mydialect.delimiter = ""
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"delimiter" must be an 1-character string')
+
+        mydialect.delimiter = b","
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"delimiter" must be string, not bytes')
 
         mydialect.delimiter = 4
-        self.assertRaises(csv.Error, mydialect)
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"delimiter" must be string, not int')
 
     def test_lineterminator(self):
         class mydialect(csv.Dialect):
@@ -796,12 +825,17 @@ class mydialect(csv.Dialect):
             lineterminator = '\r\n'
             quoting = csv.QUOTE_NONE
         d = mydialect()
+        self.assertEqual(d.lineterminator, '\r\n')
 
         mydialect.lineterminator = ":::"
         d = mydialect()
+        self.assertEqual(d.lineterminator, ":::")
 
         mydialect.lineterminator = 4
-        self.assertRaises(csv.Error, mydialect)
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"lineterminator" must be a string')
 
 
 class TestSniffer(unittest.TestCase):

Misc/NEWS

@@ -44,6 +44,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #18829: csv.Dialect() now checks type for delimiter, escapechar and
+  quotechar fields.  Original patch by Vajrasky Kok.
+
 - Issue #19855: uuid.getnode() on Unix now looks on the PATH for the
   executables used to find the mac address, with /sbin and /usr/sbin as
   fallbacks.

Modules/_csv.c

@@ -239,6 +239,12 @@ _set_char(const char *name, Py_UCS4 *target, PyObject *src, Py_UCS4 dflt)
         *target = '\0';
         if (src != Py_None) {
             Py_ssize_t len;
+            if (!PyUnicode_Check(src)) {
+                PyErr_Format(PyExc_TypeError,
+                    "\"%s\" must be string, not %.200s", name,
+                    src->ob_type->tp_name);
+                return -1;
+            }
             len = PyUnicode_GetLength(src);
             if (len > 1) {
                 PyErr_Format(PyExc_TypeError,
@@ -425,7 +431,8 @@ dialect_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
     if (dialect_check_quoting(self->quoting))
         goto err;
     if (self->delimiter == 0) {
-        PyErr_SetString(PyExc_TypeError, "delimiter must be set");
+        PyErr_SetString(PyExc_TypeError,
+                        "\"delimiter\" must be an 1-character string");
         goto err;
     }
     if (quotechar == Py_None && quoting == NULL)