From aa1c6f09560b7a90ffbe5d3aa7bb8c9409042a2f Mon Sep 17 00:00:00 2001
From: Sanjay Santhanam <51058514+Sanjays2402@users.noreply.github.com>
Date: Fri, 24 Jul 2026 18:48:54 -0700
Subject: [PATCH] Don't let the default delimiter override a caller-supplied
 dialect

CSVFormat.import_set and export_stream_set unconditionally applied
DEFAULT_DELIMITER via kwargs.setdefault. A caller passing dialect= but no
explicit delimiter= therefore got the default ',' injected alongside the
dialect, and csv gives the standalone delimiter precedence, so the dialect's
delimiter was silently ignored.

Only apply the default when no dialect was supplied. Adds a regression test
covering both the import and export paths with a sniffed ':' dialect.

Fixes #622
---
 src/tablib/formats/_csv.py |  6 ++++--
 tests/test_tablib.py       | 14 ++++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/tablib/formats/_csv.py b/src/tablib/formats/_csv.py
index e57e1d9ed..46299d127 100644
--- a/src/tablib/formats/_csv.py
+++ b/src/tablib/formats/_csv.py
@@ -18,7 +18,8 @@ def export_stream_set(cls, dataset, **kwargs):
         """Returns CSV representation of Dataset as file-like."""
         stream = StringIO()
 
-        kwargs.setdefault('delimiter', cls.DEFAULT_DELIMITER)
+        if 'dialect' not in kwargs:
+            kwargs.setdefault('delimiter', cls.DEFAULT_DELIMITER)
 
         _csv = csv.writer(stream, **kwargs)
 
@@ -40,7 +41,8 @@ def import_set(cls, dset, in_stream, headers=True, skip_lines=0, **kwargs):
 
         dset.wipe()
 
-        kwargs.setdefault('delimiter', cls.DEFAULT_DELIMITER)
+        if 'dialect' not in kwargs:
+            kwargs.setdefault('delimiter', cls.DEFAULT_DELIMITER)
 
         rows = csv.reader(in_stream, **kwargs)
         for i, row in enumerate(rows):
diff --git a/tests/test_tablib.py b/tests/test_tablib.py
index 32f0e4b15..307e4c1d4 100755
--- a/tests/test_tablib.py
+++ b/tests/test_tablib.py
@@ -1,6 +1,7 @@
 #!/usr/bin/env python
 """Tests for Tablib."""
 
+import csv
 import datetime as dt
 import doctest
 import json
@@ -1157,6 +1158,19 @@ def test_csv_formatter_support_kwargs(self):
         d2 = tablib.import_set(_csv, format="csv", **kwargs)
         self.assertEqual(3, len(d2.headers))
 
+    def test_csv_dialect_is_not_overridden_by_default_delimiter(self):
+        """A caller-supplied dialect must win over DEFAULT_DELIMITER."""
+        text = 'test:test2\nvalue1:value2\n'
+        dialect = csv.Sniffer().sniff(text.splitlines()[0])
+        self.assertEqual(':', dialect.delimiter)
+
+        imported = tablib.Dataset().load(text, format='csv', dialect=dialect)
+        self.assertEqual(['test', 'test2'], imported.headers)
+        self.assertEqual(('value1', 'value2'), imported[0])
+
+        exported = imported.export('csv', dialect=dialect)
+        self.assertEqual('test:test2\r\nvalue1:value2\r\n', exported)
+
 
 class TSVTests(BaseTestCase):
     def test_tsv_import_set(self):