gh-85052: Implement __repr__ for classes in csv module

Lib/csv.py

@@ -193,6 +193,9 @@ def __next__(self):
                 d[key] = self.restval
         return d
 
+    def __repr__(self):
+        return "%s('%s')" % (self.__class__.__name__, self.dialect)
+
     __class_getitem__ = classmethod(types.GenericAlias)
 
 
@@ -208,6 +211,7 @@ def __init__(self, f, fieldnames, restval="", extrasaction="raise",
             raise ValueError("extrasaction (%s) must be 'raise' or 'ignore'"
                              % extrasaction)
         self.extrasaction = extrasaction
+        self.dialect = dialect
         self.writer = writer(f, dialect, *args, **kwds)
 
     def writeheader(self):
@@ -228,6 +232,9 @@ def writerow(self, rowdict):
     def writerows(self, rowdicts):
         return self.writer.writerows(map(self._dict_to_list, rowdicts))
 
+    def __repr__(self):
+        return "%s('%s')" % (self.__class__.__name__, self.dialect)
+
     __class_getitem__ = classmethod(types.GenericAlias)
 
 

Lib/test/test_csv.py

@@ -204,6 +204,7 @@ class BadItem:
             def __str__(self):
                 raise OSError
         self._write_error_test(OSError, [BadItem()])
+
     def test_write_bigfield(self):
         # This exercises the buffer realloc functionality
         bigstring = 'X' * 50000
@@ -551,6 +552,19 @@ def test_roundtrip_escaped_unquoted_newlines(self):
                                                        escapechar="\\")):
                         self.assertEqual(row, rows[i])
 
+    def test_dict_reader_repr(self):
+        fileobj = StringIO()
+        reader = csv.DictReader(fileobj)
+        expected = "%s('%s')" % (reader.__class__.__name__, reader.dialect)
+        self.assertEqual(repr(reader), expected)
+
+    def test_dict_writer_repr(self):
+        fileobj = StringIO()
+        writer = csv.DictWriter(fileobj, fieldnames=[])
+        expected = "%s('%s')" % (writer.__class__.__name__, writer.dialect)
+        self.assertEqual(repr(writer), expected)
+
+
 
 class TestDialectRegistry(unittest.TestCase):
     def test_registry_badargs(self):
@@ -685,6 +699,16 @@ def test_pickle(self):
             for proto in range(pickle.HIGHEST_PROTOCOL + 1):
                 self.assertRaises(TypeError, pickle.dumps, dialect, proto)
 
+    def test_dialect_str(self):
+        for name in csv.list_dialects():
+            dialect = csv.get_dialect(name)
+            self.assertEqual(str(dialect), name)
+
+    def test_dialect_repr(self):
+        for name in csv.list_dialects():
+            dialect = csv.get_dialect(name)
+            self.assertRegex(repr(dialect), r"\w+\.Dialect\('%s'\)" % name)
+
 class TestCsvBase(unittest.TestCase):
     def readerAssertEqual(self, input, expected_result):
         with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:

Misc/NEWS.d/next/Library/2024-10-07-13-58-34.gh-issue-85052.7ZTIuX.rst

@@ -0,0 +1 @@
+Implement a ``__repr__`` method to :class:`csv.Dialect`, :class:`csv.DictReader` and :class:`csv.DictWriter`.

Modules/_csv.c

@@ -603,6 +603,34 @@ Dialect_traverse(DialectObj *self, visitproc visit, void *arg)
     return 0;
 }
 
+static PyObject *
+Dialect_str(DialectObj *self) {
+    Py_ssize_t pos = 0;
+    PyObject *key, *value;
+    PyObject *module = PyType_GetModule(Py_TYPE(self));
+    PyObject *dialects = get_csv_state(module)->dialects;
+
+    while (PyDict_Next(dialects, &pos, &key, &value)) {
+        if (value == (PyObject *)self) {
+            Py_INCREF(key);
+
+            return key;
+        }
+    }
+
+    return PyUnicode_FromString("unknown");
+}
+
+static PyObject *
+Dialect_repr(DialectObj *self) {
+    PyObject *str = Dialect_str(self);
+    PyObject *repr = PyUnicode_FromFormat("%s(%R)", Py_TYPE(self)->tp_name, str);
+
+    Py_DECREF(str);
+
+    return repr;
+}
+
 static PyType_Slot Dialect_Type_slots[] = {
     {Py_tp_doc, (char*)Dialect_Type_doc},
     {Py_tp_members, Dialect_memberlist},
@@ -612,6 +640,8 @@ static PyType_Slot Dialect_Type_slots[] = {
     {Py_tp_dealloc, Dialect_dealloc},
     {Py_tp_clear, Dialect_clear},
     {Py_tp_traverse, Dialect_traverse},
+    {Py_tp_str, Dialect_str},
+    {Py_tp_repr, Dialect_repr},
     {0, NULL}
 };