bpo-20028: Empty escapechar/quotechar is not allowed for csv.Dialect

Author: corona10

Doc/library/csv.rst

@@ -383,6 +383,8 @@ Dialects support the following attributes:
    :const:`False`. On reading, the *escapechar* removes any special meaning from
    the following character. It defaults to :const:`None`, which disables escaping.
 
+   .. versionchanged:: 3.11
+      An empty *escapechar* is not allowed.
 
 .. attribute:: Dialect.lineterminator
 
@@ -402,6 +404,8 @@ Dialects support the following attributes:
    as the *delimiter* or *quotechar*, or which contain new-line characters.  It
    defaults to ``'"'``.
 
+   .. versionchanged:: 3.11
+      An empty *quotechar* is not allowed.
 
 .. attribute:: Dialect.quoting
 

Lib/test/test_csv.py

@@ -913,6 +913,12 @@ class mydialect(csv.Dialect):
         self.assertEqual(d.quotechar, '"')
         self.assertTrue(d.doublequote)
 
+        mydialect.quotechar = ""
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"quotechar" must be a 1-character string')
+
         mydialect.quotechar = "''"
         with self.assertRaises(csv.Error) as cm:
             mydialect()
@@ -977,6 +983,10 @@ class mydialect(csv.Dialect):
         d = mydialect()
         self.assertEqual(d.escapechar, "\\")
 
+        mydialect.escapechar = ""
+        with self.assertRaisesRegex(csv.Error, '"escapechar" must be a 1-character string'):
+            mydialect()
+
         mydialect.escapechar = "**"
         with self.assertRaisesRegex(csv.Error, '"escapechar" must be a 1-character string'):
             mydialect()

Misc/NEWS.d/next/Library/2021-10-10-00-25-36.bpo-20028.bPx4Z8.rst

@@ -0,0 +1,2 @@
+Empty escapechar/quotechar is not allowed when initializing
+:class:`csv.Dialect`. Patch by Vajrasky Kok and Dong-hee Na.

Modules/_csv.c

@@ -250,7 +250,7 @@ _set_char_or_none(const char *name, Py_UCS4 *target, PyObject *src, Py_UCS4 dflt
             if (len < 0) {
                 return -1;
             }
-            if (len > 1) {
+            if (len != 1) {
                 PyErr_Format(PyExc_TypeError,
                     "\"%s\" must be a 1-character string",
                     name);
@@ -283,7 +283,7 @@ _set_char(const char *name, Py_UCS4 *target, PyObject *src, Py_UCS4 dflt)
         if (len < 0) {
             return -1;
         }
-        if (len > 1) {
+        if (len != 1) {
             PyErr_Format(PyExc_TypeError,
                          "\"%s\" must be a 1-character string",
                          name);