Issue #5006: Better handling of unicode byte-order marks (BOM) in the io library.
This means, for example, that opening an UTF-16 text file in
append mode doesn't add a BOM at the end of the file if the file isn't
empty.
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 1a525dc..98dc711 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -1963,6 +1963,37 @@
self.assertEqual(buffer.seekable(), txt.seekable())
+ def test_append_bom(self):
+ # The BOM is not written again when appending to a non-empty file
+ filename = support.TESTFN
+ for charset in ('utf-8-sig', 'utf-16', 'utf-32'):
+ with self.open(filename, 'w', encoding=charset) as f:
+ f.write('aaa')
+ pos = f.tell()
+ with self.open(filename, 'rb') as f:
+ self.assertEquals(f.read(), 'aaa'.encode(charset))
+
+ with self.open(filename, 'a', encoding=charset) as f:
+ f.write('xxx')
+ with self.open(filename, 'rb') as f:
+ self.assertEquals(f.read(), 'aaaxxx'.encode(charset))
+
+ def test_seek_bom(self):
+ # Same test, but when seeking manually
+ filename = support.TESTFN
+ for charset in ('utf-8-sig', 'utf-16', 'utf-32'):
+ with self.open(filename, 'w', encoding=charset) as f:
+ f.write('aaa')
+ pos = f.tell()
+ with self.open(filename, 'r+', encoding=charset) as f:
+ f.seek(pos)
+ f.write('zzz')
+ f.seek(0)
+ f.write('bbb')
+ with self.open(filename, 'rb') as f:
+ self.assertEquals(f.read(), 'bbbzzz'.encode(charset))
+
+
class CTextIOWrapperTest(TextIOWrapperTest):
def test_initialization(self):